Method, apparatus, and system for physical channel transmission in unlicensed band

ABSTRACT

A user equipment of a wireless communication system is disclosed. The user equipment includes a communication module, and a processor. The processor is configured to transmit a radio frame divided into a plurality of subframes through the communication module, and perform a UL transmission in a partial subframe having a duration shorter than one subframe duration to the base station based on at least one of an indication of a base station and a result of a channel access of the wireless communication system.

TECHNICAL FIELD

The present invention relates to a wireless communication system.Specifically, the present invention relates to a method, device, andsystem for transmitting physical channels in an unlicensed band.

BACKGROUND ART

In recent years, with an explosive increase of mobile traffic due to thespread of smart devices, it has been difficult to cope with data usagewhich increases for providing a cellular communication service only by aconventional licensed frequency spectrum or LTE-licensed frequency band.

In such a situation, a scheme that uses an unlicensed frequency spectrumor LTE-Unlicensed frequency band (e.g., 2.4 GHz band, 5 GHz band, or thelike) for providing the cellular communication service has been devisedas a solution for a spectrum shortage problem.

However, unlike the licensed band in which a communication serviceprovider secures an exclusive frequency use right through a proceduresuch as auction, or the like, in the unlicensed band, multiplecommunication facilities can be used simultaneously without limit whenonly a predetermined level of adjacent band protection regulation isobserved. As a result, when the unlicensed band is used in the cellularcommunication service, it is difficult to guarantee communicationquality at a level provided in the licensed band and an interferenceproblem with a conventional wireless communication device (e.g.,wireless LAN device) using the unlicensed band may occur.

Therefore, a research into a coexistence scheme with the conventionalunlicensed band device and a scheme for efficiently sharing a radiochannel needs to be preferentially made in order to settle an LTEtechnology in the unlicensed band. That is, a robust coexistencemechanism (RCM) needs to be developed in order to prevent a device usingthe LTE technology in the unlicensed band from influencing theconventional unlicensed band device.

DISCLOSURE Technical Problem

It is an object of the present invention to provide a method and devicefor efficiently transmitting a signal in a wireless communicationsystem, in particular, a cellular wireless communication system. It isanother object of the present invention to provide a method and devicefor efficiently transmitting a signal in a specific frequency band(e.g., unlicensed band). In particular, it is an object of the presentinvention to provide a method and device for efficiently transmitting aphysical channel in a specific frequency band.

The technical object of the present invention is not limited to theabove technical objects, and other technical problems that are notmentioned will be apparent to those skilled in the art from thefollowing description.

Technical Solution

According to an embodiment of the present invention, a user equipment ofa wireless communication system includes a communication module; and aprocessor. The processor is configured to perform UL transmissionincluding a single or a plurality of subframes through the communicationmodule. In this case, the processor is configured to perform uplink (UL)transmission including a single or a plurality of subframes through thecommunication module, and performs UL transmission in a partial subframehaving a duration shorter than a duration of one subframe to a basestation according to at least one of an indication of the base stationand a result of a channel access of the wireless communication system.In this case, the UL transmission may include transmission of a ULchannel. In addition, the UL transmission may include transmission of areference signal.

The processor, when the user equipment accesses a channel using achannel access based random backoff, may be configured to adjust a valueof a contention window used in the channel access based random backoffbased on whether a transmission of a reference subframe previouslytransmitted by the user equipment using the channel access based randombackoff is successful or not, and attempt UL transmission to the basestation by accessing the channel based on the value of the contentionwindow. In this case, the reference subframe may include the partialsubframe. In addition, the contention window may indicate a range inwhich a natural number that determines a backoff time in a procedure ofthe channel access based random backoff is obtained randomly, and thevalue of the contention window may be the largest value among valuesthat the natural number is capable of having.

The processor, when an earliest subframe among one or more firstsubframes that are continuously transmitted, by the user equipment,without a gap before a recently transmitted subframe and perform a ULtransmission is the partial subframe, may be configured to determine, asthe reference subframe, the earliest subframe and a subframe transmittedby the user equipment immediately after the earliest subframe among theone or more first subframes. In this case, the recently transmittedsubframe may be a subframe that is transmitted most recently by the userequipment among subframes that are transmitted by the user equipmentbefore a time point obtained by subtracting a predetermined timeinterval from a starting time point of a subframe including a UL grantand perform a UL transmission. In addition, the UL grant may indicate aUL transmission to the base station, which is attempted by accessing thechannel based on a size of the contention window.

When the recently transmitted subframe is the partial subframe and thereare no one or more first subframes, the processor may be configured todetermine only the recently transmitted subframe as the referencesubframe.

The recently transmitted subframe may be the partial subframe, there maybe no one or more first subframes, and there may be one or more secondsubframes that are continuously transmitted, by the user equipment,without a gap after the recently transmitted subframe and perform a ULtransmission. In this case, the processor may be configured to determinethe recently transmitted subframe and a next subframe of the recentlytransmitted subframe among the one or more second subframes as thereference subframe.

when a new data indicator (NDI) for at least one HARQ process associatedwith at least one reference hybrid automatic repeat request (HARQ)process identifier (ID) is toggled, the processor may be configured toset a value of a contention window of all channel access priorityclasses to a minimum value of a value of a contention windowcorresponding to each channel access priority classes. In this case, thereference HARQ process ID may be an identifier for identifying an HARQprocess of a UL-SCH in the reference subframe.

When a new data indicator (NDI) for at least one HARQ process associatedwith at least one reference hybrid automatic repeat request (HARQ)process identifier (ID) is not toggled, the processor may be configuredto increase a value of a contention window of all channel accesspriority classes to a next greater value than a current value of acontention window among values allowed in a corresponding channel accesspriority class.

When a UL grant indicates that the user equipment is capable of startinga UL transmission to the base station at a subframe boundary and atleast one transmission starting time point in a subframe, and the userequipment fails to access the channel to fail to start a UL transmissionto the base station until the initial starting time point oftransmission, the processor may be configured to attempt a channelaccess for a UL transmission to the base station before remainingstarting time points of transmission other than the initial startingtime point of transmission.

When the user equipment fails to access a channel to fail to start theUL transmission to the base station until the initial starting timepoint of transmission, the processor may be configured to determine achannel access type used in a channel access for a UL transmission tothe base station after the initial starting time point of transmissionbased on whether the user equipment performs a transmission within amaximum channel occupancy time (MCOT) configured by the base station.

When the user equipment fails to access the channel fails to start theUL transmission to the base station until the initial starting timepoint of transmission and the user equipment performs the transmissionwithin the MCOT configured by the base station, the processor may beconfigured to attempt to access a channel for UL transmission for thebase station based on whether the channel is idle for a predeterminedsingle time interval after the first transmission starting time point.

When the user equipment fails to access a channel and fails to starttransmission for the base station until the initial starting time pointof transmission, the processor may be configured to determine a channelaccess type used in channel access for the UL transmission to the basestation after the initial starting time point of transmission based onwhether the user equipment performs the transmission in the MCOTconfigured by the base station, regardless of the channel access typeindicated by a UL grant indicating the UL transmission after the initialstarting time point of transmission from the base station.

When the user equipment fails to access the channel to fails to startthe UL transmission to the base station until the initial starting timepoint of transmission, the processor may be configured to access thechannel for the UL transmission for the base station after the initialstarting time point of transmission, regardless of the channel accesstype indicated by the UL grant indicating the UL transmission after theinitial starting time point of transmission from the base station.

The channel access type may include a first type indicating a channelaccess based random backoff and a second type indicating channel accessin which channel access is performed based on whether the channel isidle for a predetermined single time interval.

When the user equipment transmits a last subframe of a UL transmissionto the base station as the partial subframe, the processor may beconfigured to configure the partial subframe starting from a SingleCarrier (SC)-Frequency Division Multiple Access (FDMA) index 0 to anSC-FDMA symbol having an SC-FDMA symbol index of 3, 6, or 10, and endthe UL transmission to the base station by transmitting the configuredpartial subframe.

The processor may be configured to transmit a Demodulation-ReferenceSignal (DM-RS) at an SC-FDMA symbol position having an SC-FDMA symbolindex of 3 or 10 in a subframe.

According to an embodiment of the present invention, an operation methodof a user equipment of a wireless communication system includesperforming uplink (UL) transmission including a single or a plurality ofsubframes. In this case, the performing the UL transmission may includeperforming the UL transmission in a partial subframe having a durationshorter than a duration of one subframe to a base station according toat least one of an indication of the base station and a result ofchannel access of the wireless communication system. In this case, theUL transmission may include transmission of a UL channel. In addition,the UL transmission may include transmission of a reference signal.

The method may further include, when the user equipment accesses achannel using a channel access based random backoff, adjusting a valueof a contention window used in the channel access based random backoffbased on whether a transmission of a reference subframe previouslytransmitted by the user equipment using the channel access based randombackoff is successful or not, and attempting a UL transmission to thebase station by accessing the channel based on the value of thecontention window. In this case, the reference subframe may include thepartial subframe. In addition, the contention window may indicate arange in which a natural number that determines a backoff time in aprocedure of the channel access based random backoff is obtainedrandomly, and the value of the contention window may be the largestvalue among values that the natural number is capable of having.

The adjusting the value of the contention window may include, when theearliest subframe among one or more first subframes that arecontinuously transmitted, by the user equipment, without a gap before arecently transmitted subframe and perform a UL transmission is thepartial subframe, determining, as the reference subframe, the earliestsubframe and a subframe transmitted by the user equipment immediatelyafter the earliest subframe among the one or more first subframes. Inthis case, the recently transmitted subframe may be a subframe that istransmitted most recently by the user equipment among subframes that aretransmitted by the user equipment before a time point obtained bysubtracting a predetermined time interval from a starting time point ofa subframe including a UL grant and perform UL transmission. Inaddition, the UL grant may indicate a UL transmission for the basestation, which is attempted by accessing a channel based on the size ofthe contention window.

The adjusting the value of the contention window may further include,when there are no one or more first subframes, determining only therecently transmitted subframe as the reference subframe.

The adjusting the value of the contention window may further include,when there are no one or more first subframes, and there are one or moresecond subframes that are continuously transmitted, by the userequipment, without a gap after the recently transmitted subframe andperform a UL transmission, determining the recently transmitted subframeand a next subframe of the recently transmitted subframe among the oneor more second subframes as the reference subframe.

Advantageous Effects

A wireless communication system according to an embodiment of thepresent invention, in particular, a cellular wireless communicationsystem provides a method and device for efficiently transmittingsignals. In addition, the wireless communication system according to anembodiment of the present invention provides a method and device forefficiently transmitting a signal in a specific frequency band (e.g.,unlicensed band). In addition, the wireless communication systemaccording to an embodiment of the present invention provides a methodand device for efficiently transmitting control channels in a specificfrequency band (e.g., unlicensed band).

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates physical channels used in a 3rd generationpartnership project (3GPP) system and a general signal transmittingmethod using the physical channels.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system.

FIG. 3 illustrates one example of a downlink (DL)/uplink (UL) slotstructure in the wireless communication system.

FIG. 4 illustrates a structure of a downlink subframe.

FIG. 5 illustrates a structure of an uplink subframe.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication.

FIG. 7 illustrates an example in which a cross carrier schedulingtechnique is applied.

FIG. 8 illustrates Discovery Reference Signal (DRS) transmission.

FIGS. 9 to 11 illustrate the structure of a reference signal used asDRS.

FIG. 12 illustrates a Licensed Assisted Access (LAA) serviceenvironment.

FIG. 13 illustrates a deployment scenario of a user equipment and a basestation in an LAA service environment.

FIG. 14 illustrates a conventional communication scheme operating in anunlicensed band.

FIGS. 15 and 16 illustrate a Listen-Before-Talk (LBT) procedure for DLtransmission.

FIG. 17 shows a resource used by a base station after an LBT procedurein an unlicensed band according to an embodiment of the presentinvention.

FIG. 18 shows a method of a base station to transmit a control channelfor scheduling partial subframes after an LBT procedure in an unlicensedband according to an embodiment of the present invention.

FIG. 19 shows a method of a base station to transmit a control channelfor scheduling super subframes after an LBT procedure in an unlicensedband according to an embodiment of the present invention.

FIG. 20 shows another method of a base station to transmit a controlchannel for scheduling super subframes after an LBT procedure in anunlicensed band according to an embodiment of the present invention.

FIG. 21 shows a method of a base station to transmit a control channelfor scheduling a subframe having a boundary different from a boundary ofsubframe of a PCell after the LBT procedure in the unlicensed bandaccording to an embodiment of the present invention.

FIG. 22 shows another method of a base station to transmit a controlchannel for scheduling super subframes after an LBT procedure in anunlicensed band according to an embodiment of the present invention.

FIG. 23 shows an UL subframe structure transmitted by a user equipmentaccording to an embodiment of the present invention.

FIGS. 24 and 25 show that a user equipment is configured to receive anstarting partial subframe of UL transmission from a base station andperforms UL transmission to the base station according to an embodimentof the present invention.

FIGS. 26 and 27 show that a user equipment is configured to receive anending partial subframe that ends UL transmission from a base stationand performs UL transmission to the base station according to anembodiment of the present invention.

FIGS. 28 to 30 show operation of determining, by a user equipment, areference subframe of CWS adjustment based on a subframe including an ULgrant.

FIG. 31 is a flowchart illustrating an operation of a user equipmentaccording to an embodiment of the present invention.

FIG. 32 shows a configuration of a user equipment and a base stationaccording to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used as possible by considering functions in the presentinvention, but the terms may be changed depending on an intention ofthose skilled in the art, customs, and emergence of new technology.Further, in a specific case, there is a term arbitrarily selected by anapplicant and in this case, a meaning thereof will be described in acorresponding description part of the invention. Accordingly, it intendsto be revealed that a term used in the specification should be analyzedbased on not just a name of the term but a substantial meaning of theterm and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “equal to or more than” or “equal to orless than” based on a specific threshold may be appropriatelysubstituted with “more than” or “less than”, respectively in someexemplary embodiments.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), and the like. The CDMA may be implemented by a radiotechnology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA may be implemented by a radio technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMAmay be implemented by a radio technology such as IEEE 802.11(Wi-Fi),IEEE 802.16(WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3^(rd) generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) and LTE-advanced (A) is an evolvedversion of the 3GPP LTE. 3GPP LTE/LTE-A is primarily described for cleardescription, but technical spirit of the present invention is notlimited thereto.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2017-0038005 (2017 Mar. 25), Nos. 10-2017-0102374(2017 Aug. 11), and Nos. 10-2017-0151749 (2017 Nov. 14) filed in theKorean Intellectual Property Office and the embodiments and mentioneditems described in the respective applications are included in theDetailed Description of the present application.

FIG. 1 illustrates physical channels used in a 3GPP system and a generalsignal transmitting method using the physical channels. A user equipmentreceives information from a base station through downlink (DL) and theuser equipment transmits information through uplink (UL) to the basestation. The information transmitted/received between the base stationand the user equipment includes data and various control channel andvarious physical channels exist according to a type/purpose of theinformation transmitted/received between the base station and the userequipment.

When a power of the user equipment is turned on or the user equipmentnewly enters a cell, the user equipment performs an initial cell searchoperation including synchronization with the base station, and the like(S101). To this end, the user equipment receives a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the base station to synchronize with the base station andobtain information including a cell ID, and the like. Thereafter, theuser equipment receives a physical broadcast channel from the basestation to obtain intra-cell broadcast information. The user equipmentreceives a downlink reference signal (DL RS) in an initial cell searchstep to verify a downlink channel state.

The user equipment that completes initial cell search receives aphysical downlink control channel (PDCCH) and a physical downlink sharedchannel (PDSCH) depending on information loaded on the PDCCH to obtainmore detailed system information (S102).

When there is no radio resource for initially accessing the base stationor signal transmission, the user equipment may perform a random accessprocedure (RACH procedure) to the base station (S103 to S106). Firstly,the user equipment may transmit a preamble through a physical randomaccess channel (PRACH) (S103) and receive a response message to thepreamble through the PDCCH and the PDSCH corresponding thereto (S104).When the user equipment receive a valid response message to randomaccess, the user equipment may transmit data including an identifier ofthe user equipment to the base station by using the uplink (UL) grant(S105). To resolve a contention resolution, the user equipment may waitfor receiving PDCCH as instruction of the base station. When the userequipment receive PDCCH by using the identifier of the user equipment(S016), random access procedure may end.

Thereafter, the user equipment may receive the PDCCH/PDSCH (S107) andtransmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S108) as a general procedure. The userequipment receives downlink control information (DCI) through thecontrol channel (PDCCH or E-PDCCH). The DCI includes control informationsuch as resource allocation information to the user equipment and aformat varies depending on a use purpose. The control information whichthe user equipment transmits to the base station is designated as uplinkcontrol information (UCI). The UCI includes an acknowledgement/negativeacknowledgement (ACK/NACK), a channel quality indicator (CQI), aprecoding matrix index (PMI), a rank indicator (RI), and the like. TheUCI may be transmitted through the PUSCH and/or PUCCH.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system. FIG. 2A illustrates a frame structure forfrequency division duplex (FDD) and FIG. 2B illustrates a framestructure for time division duplex (TDD).

Referring to FIG. 2, a radio frame may have a length of 10 ms (307200Ts) and be constituted by 10 subframes (SFs). Ts represents a samplingtime and is expressed as Ts=1/(2048*15 kHz). Each subframe may have alength of 1 ms and be constituted by 2 slots. Each slot has a length of0.5 ms. 20 slots in one radio frame may be sequentially numbered from 0to 19. A time for transmitting one subframe is defined as a transmissiontime interval (TTI). A time resource may be distinguished by radio framenumbers/indexes, subframe numbers/indexes #0 to #9, and slotnumbers/indexes #0 to #19.

The radio frame may be configured differently according to a duplexmode. In an FDD mode, downlink transmission and uplink transmission aredistinguished by a frequency and the radio frame includes only one of adownlink subframe and an uplink subframe with respect to a specificfrequency band. In a TDD mode, the downlink transmission and the uplinktransmission are distinguished by a time and the radio frame includesboth the downlink subframe and the uplink subframe with respect to aspecific frequency band. The TDD radio frame further includes specialsubframes for downlink and uplink switching. The special subframeincludes a Downlink Pilot Time Slot (DwPTS), a guard period (GP), and anUplink Pilot Time Slot (UpPTS).

FIG. 3 illustrates a structure of a downlink/uplink slot.

Referring to FIG. 3, the slot includes a plurality of orthogonalfrequency divisional multiplexing (OFDM) symbols in a time domain and aplurality of resource blocks (RB s) in a frequency domain. The OFDMsymbol also means one symbol period. The OFDM symbol may be called anOFDMA symbol, a single carrier frequency division multiple access(SC-FDMA) symbol, or the like according to a multi-access scheme. Thenumber of OFDM symbols included in one slot may be variously modifiedaccording to the length of a cyclic prefix (CP). For example, in thecase of a normal CP, one slot includes 7 OFDM symbols and in the case ofan extended CP, one slot includes 6 OFDM symbols. The RB is defined asN^(DL/UL) _(symb) (e.g., 7) continuous OFDM symbols in the time domainand N^(RB) _(sc) (e.g., 12) continuous subcarriersin the frequencydomain. A resource constituted by one OFDM symbol and one subcarrier isreferred to as a resource element (RE) or a tone. One RB is constitutedby N^(DL/UL) _(symb)*N^(RB) _(sc) resource elements.

The resource of the slot may be expressed as a resource grid constitutedby N^(DL/UL) _(symb)*N^(RB) _(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. Each RE in the resource grid is uniquely defined by an indexpair (k, 1) for each slot. k represents an index given with 0 toN^(DL/UL) _(RB)*N^(RB) _(sc)−1 in the frequency domain and l representsan index given with 0 to N^(DL/UL) _(symb)−1 in the time domain. Herein,N^(DL) _(RB) represents the number of resource blocks (RBs) in thedownlink slot and N^(UL) _(RB) represents the number of RBs in the ULslot. N^(DL) _(RB) and N^(UL) _(RB) depend on a DL transmissionbandwidth and a UL transmission bandwidth, respectively. N^(DL) _(symb)represents the number of symbols in the downlink slot and N^(UL) _(symb)represents the number of symbols in the UL slot. N^(RB) _(sc) representsthe number of subcarriers constituting one RB. One resource grid isprovided per antenna port.

FIG. 4 illustrates a structure of a downlink subframe.

Referring to FIG. 4, the subframe may be constituted by 14 OFDM symbols.First 1 to 3 (alternatively, 2 to 4) OFDM symbols are used as a controlregion and the remaining 13 to 11 (alternatively, 12 to 10) OFDM symbolsare used as a data region according to subframe setting. R1 to R4represent reference signals for antenna ports 0 to 3. Control channelsallocated to the control region include a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), a physical downlink control channel (PDCCH), and the like. Datachannels allocated to the data region include the PDSCH, and the like.When an enhanced PDCCH (EPDCCH) is set, the PDSCH and the EPDCCH aremultiplexed by frequency division multiplexing (FDM) in the data region.

The PDCCH as the physical downlink control channel is allocated to firstn OFDM symbols of the subframe. n as an integer of 1 (alternatively, 2)or more is indicated by the PCFICH. The PDCCH announces informationassociated with resource allocation of a paging channel (PCH) and adownlink-shared channel (DL-SCH) as transmission channels, an uplinkscheduling grant, HARQ information, and the like to each user equipmentor user equipment group. Data (that is, transport block) of the PCH andthe DL-SCH are transmitted through the PDSCH. Each of the base stationand the user equipment generally transmit and receive data through thePDSCH except for specific control information or specific service data.

Information indicating to which user equipment (one or a plurality ofuser equipments) the data of the PDSCH is transmitted, informationindicating how the user equipments receive and decode the PDSCH data,and the like are transmitted while being included in the PDCCH/EPDCCH.For example, it is assumed that the PDCCH/EPDCCH is CRC-masked with aradio network temporary identity (RNTI) called “A” and informationregarding data transmitted by using a radio resource (e.g., frequencylocation) called “B” and a DCI format called “C”, that is, transmissionformat information (e.g., transport block size, modulation scheme,coding information, and the like) is transmitted through a specificsubframe. In this case, a user equipment in the cell senses thePDCCH/EPDCCH by using the RNTI information thereof and when one or moreuser equipments having the “A” RNTI are provided, the user equipmentsreceive the PDCCH/EPDCCH and receive the PDSCH indicated by “B” and “C”through information on the received PDCCH/EPDCCH.

FIG. 5 illustrates a structure of an uplink subframe.

Referring to FIG. 5, the subframe may be divided into the control regionand the data region in the frequency domain. The PUCCH is allocated tothe control region and carries the UCI. The PUSCH is allocated to thedata region and carries user data.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling Request (SR): Information used to request a UL-SCH        resource. The SR is transmitted by using an on-off keying (OOK)        scheme.    -   HARQ-ACK: Response to the PDCCH and/or response to a downlink        data packet (e.g., codeword) on the PDSCH. The codeword is an        encoded format of the transport block. The HARQ-ACK indicates        whether the PDCCH or PDSCH is successfully received. The        HARQ-ACK response includes a positive ACK (simply, ACK), a        negative ACK (NACK), discontinuous transmission (DTX), or the        NACK/DTX. The DTX represents a case in which the user equipment        misses the PDCCH (alternatively, semi-persistent scheduling        (SPS) PDSCH) and the NACK/DTX means the NACK or DTX. The        HARQ-ACK is mixedly used with the HARQ-ACK/NACK and the        ACK/NACK.    -   Channel State Information (CSI): Feed-back information regarding        the downlink channel. Multiple input multiple output (MIMO)        related feed-back information includes the RI and the PMI.

Table 1 shows the relationship between a PUCCH format and the UCI.

TABLE 1 PUCCH Format Uplink control information (UCI) Format 1Scheduling request (SR) (non-modulated waveform) Format 1a 1-bit HARQACK/NACK (SR existence/non-existence) Format 1b 2-bit HARQ ACK/NACK (SRexistence/non-existence) Format 2 CSI (20 coded bits) Format 2 CSI and 1or 2-bit HARQ ACK/NACK (20 bits) (corresponding to only extended CP)Format 2a CSI and 1-bit HARQ ACK/NACK (20 + 1 coded bits) Format 2b CSIand 2-bit HARQ ACK/NACK (20 + 2 coded bits) Format 3 HARQ ACK/NACK + SR(48 coded bits) (LTE-A)

Hereinafter, carrier aggregation will be described. The carrieraggregation means a method in which the wireless communication systemuses a plurality of frequency blocks as one large logical frequency bandin order to use a wider frequency band. When a whole system band isextended by the carrier aggregation, a frequency band used forcommunication with each user equipment is defined by a component carrier(CC) unit.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication. FIG. 6(a) illustrates a subframe structureof a single carrier and

FIG. 6(b) illustrates a subframe structure of multi-carriers which arecarrier-aggregated.

Referring to FIG. 6(a), in a single carrier system, the base station andthe user equipment perform data communication through one DL band andone UL band corresponding thereto. The DL/UL band is divided into aplurality of orthogonal subcarriers and each frequency band operates atone carrier frequency. In the FDD, the DL and UL bands operate atdifferent carrier frequencies, respectively and in the TDD, the DL andUL bands operate at the same carrier frequency. The carrier frequencymeans a center frequency of the frequency band.

Referring to FIG. 6(b), the carrier aggregation is distinguished from anOFDM system that performs DL/UL communication in a base frequency banddivided into a plurality of subcarriers by using one carrier frequency,in that the carrier aggregation performs DL/UL communication by using aplurality of carrier frequencies. Referring to FIG. 6(b), three 20 MHzCCs are gathered in each of the UL and the DL to support a bandwidth of60 MHz. The CCs may be adjacent to each other or non-adjacent to eachother in the frequency domain. For convenience, FIG. 6(b) illustrates acase in which a bandwidth of a UL CC and a bandwidth of a DL CC are thesame as each other and symmetric to each other, but the bandwidths ofthe respective CCs may be independently decided. Further, asymmetriccarrier aggregation in which the number of UL CCs and the number of DLCCs are different from each other is also available. The DL/UL CC(s) areindependently allocated/configured for each user equipment and the DL/ULCC(s) allocated/configured to the user equipment are designated asserving UL/DL CC(s) of the corresponding user equipment.

The base station may activate some or all of serving CCs of the userequipment or deactivate some CCs. When the base station allocates theCC(s) to the user equipment, if the CC allocation to the user equipmentis wholly reconfigured or if the user equipment does not hand over, atleast one specific CC among the CC(s) configured with respect to thecorresponding user equipment is not deactivated. A specific CC which isalways activated is referred to as a primary CC (PCC) and a CC which thebase station may arbitrarily activate/deactivate is referred to as asecondary CC (SCC). The PCC and the SCC may be distinguished based onthe control information. For example, specific control information maybe set to be transmitted/received only through a specific CC and thespecific CC may be referred to as the PCC and remaining CC(s) may bereferred to as SCC(s). The PUCCH is transmitted only on the PCC.

In 3GPP, a concept of the cell is used in order to manage the radioresource. The cell is defined as a combination of the DL resource andthe UL resource, that is, a combination of the DL CC and the UL CC. Thecell may be configured by the DL resource only or the combination of theDL resource and the UL resource. When the carrier aggregation issupported, a linkage between the carrier frequency of the DL resource(alternatively, DL CC) and the carrier frequency of the UL resource(alternatively, UL CC) may be indicated by system information. Forexample, the combination of the DL resource and the UL resource may beindicated by a system information block type 2 (SIB2) linkage. Thecarrier frequency means a center frequency of each cell or CC. A cellcorresponding to the PCC is referred to as the primary cell (PCell) anda cell corresponding to the SCC is referred to as the secondary cell(SCell). A carrier corresponding to the PCell is a DL PCC in thedownlink and a carrier corresponding to the PCell is a UL PCC in theuplink. Similarly, a carrier corresponding to the SCell is a DL SCC inthe downlink and a carrier corresponding to the SCell is a UL SCC in theuplink. According to a user equipment capability, the serving cell(s)may be constituted by one PCell and 0 or more SCells. For a userequipment which is in an RRC_CONNECTED state, but does not have anyconfiguration for the carrier aggregation or does not support thecarrier aggregation, only one serving cell constituted by only the PCellis present.

FIG. 7 illustrates an example in which cross carrier scheduling isapplied. When the cross carrier scheduling is configured, a controlchannel transmitted through a first CC may schedule a data channeltransmitted through the first CC or a second CC by using a carrierindicator field (CIF). The CIF is included in the DCI. In other words, ascheduling cell is configured, and a DL grant/UL grant transmitted in aPDCCH area of the scheduling cell schedules the PDSCH/PUSCH of ascheduled cell. That is, a search space for a plurality of componentcarriers is present in the PDCCH area of the scheduling cell. The PCellmay be basically the scheduling cell and a specific SCell may bedesignated as the scheduling cell by an higher layer.

In FIG. 7, it is assumed that three DL CCs are aggregated. Herein, DLcomponent carrier #0 is assumed as the DL PCC (alternatively, PCell) andDL component carrier #1 and DL component carrier #2 are assumed as theDL SCC (alternatively, SCell). Further, it is assumed that the DL PCC isset as a PDCCH monitoring CC. When the CIF is disabled, the respectiveDL CCs may transmit only the PDCCH that schedules the PDSCH thereofwithout the CIF according to an LTE PDCCH rule (non-cross carrierscheduling or self-carrier scheduling). On the contrary, when the CIF isenabled by UE-specific (alternatively, UE-group-specific orcell-specific) higher layer signaling, a specific CC (e.g., DL PCC) maytransmit the PDCCH scheduling the PDSCH of DL CC A and the PDCCHscheduling the PDSCH of another CC by using the CIF (cross-carrierscheduling). On the contrary, in another DL CC, the PDCCH is nottransmitted.

Hereinafter, DRS transmission in a licensed band will be described withreference to FIGS. 8 to 11. FIG. 8 illustrates DRS transmission, andFIGS. 9 to 11 illustrate a structure of a reference signal used in DRS.For convenience, DRS in the licensed band is referred to as Rel-12 DRS.DRS supports small cell on/off, and a SCell that is not active for anyuser equipment may be turned off except for DRS periodic transmission.Also, based on the DRS, a user equipment may obtain cell identificationinformation, measure Radio Resource Management (RRM), and obtaindownlink synchronization.

Referring to FIG. 8, a Discovery Measurement Timing Configuration (DMTC)indicates a time window in which a user equipment expects to receiveDRS. The DMTC is fixed at 6 ms. The DMTC period is the transmissionperiod of the DMTC, and may be 40 ms, 80 ms, or 160 ms. The position ofthe DMTC is specified by the DMTC transmission period and the DMTCoffset (in units of subframes), and these information are transmitted tothe user equipment through higher layer signaling (e.g., RRC signaling).DRS transmissions occur at the DRS occasion within the DMTC. The DRSoccasion has a transmission period of 40 ms, 80 ms or 160 ms, and theuser equipment may assume that there is one DRS occasion per DMTCperiod. The DRS occasion includes 1 to 5 consecutive subframes in theFDD radio frame and 2 to 5 consecutive subframes in the TDD radio frame.The length of the DRS occasion is delivered to the user equipment viahigher layer signaling (e.g., RRC signaling). The user equipment mayassume DRS in the DL subframe in the DRS occasion. DRS occasion mayexist anywhere in the DMTC, but the user equipment expects thetransmission interval of DRSs transmitted from the cell to be fixed(i.e., 40 ms, 80 ms, or 160 ms). That is, the position of the DRSoccasion in the DMTC is fixed per cell. The DRS is configured asfollows.

-   -   Cell-specific Reference Signal (CRS) at antenna port 0 (see FIG.        9): It exists in all downlink subframes within the DRS occasion,        and in the DwPTS of all the special subframes. The CRS is        transmitted in the entire band of the subframe.    -   Primary Synchronization Signal (PSS) (see FIG. 10): In the case        of FDD radio frame, it exists in the first subframe in DRS        occasion, or in the second subframe in DRS occasion in the case        of TDD radio frame. The PSS is transmitted in the seventh (or        sixth) OFMDA symbol of the subframe and mapped to six RBs (=72        subcarriers) close to the center frequency.    -   Secondary Synchronization Signal (SSS) (see FIG. 10): It exists        in the first subframe in the DRS occasion. The SSS is        transmitted in the sixth (or fifth) OFMDA symbol of the subframe        and mapped to six RBs (=72 subcarriers) close to the center        frequency.    -   non-zero-power Channel State Information (CSI)-RS (see FIG. 11):        It exists in zero or more subframes in the DRS occasion. The        position of the non-zero-power CSI-RS is variously configured        according to the number of CSI-RS ports and the higher layer        configuration information.

FIG. 8 illustrates a case where the DRS reception time is set to aseparate DMTC for each frequency in a user equipment's situation.Referring to FIG. 8, in the case of frequency F1, a DRS occasion with alength of 2 ms is transmitted every 40 ms, in the case of frequency F2,a DRS occasion with a length of 3 ms is transmitted every 80 ms, and inthe case of frequency F3, a DRS occasion with a length of 4 ms istransmitted every 80 ms. The user equipment may know the startingposition of the DRS occasion in the DMTC from the subframe including theSSS. Here, the frequencies F1 to F3 may be replaced with correspondingcells, respectively.

Embodiment: DRS Transmission Scheme in Unlicensed Band

FIG. 12 illustrates a Licensed Assisted Access (LAA) serviceenvironment. Referring to FIG. 12, a service environment in which LTEtechnology 11 in the existing licensed band and LTE-Unlicensed (LTE-U),i.e., LTE technology 12 in the unlicensed band currently being activelydiscussed, or LAA are incorporated may be provided to a user.

FIG. 13 illustrates a deployment scenario of a user equipment and a basestation in an LAA service environment.

A frequency band targeted by the LAA service environment has short radiocommunication range due to the high frequency characteristics.Considering this, the deployment scenario of the user equipment and thebase station may be an overlay model or a co-located model in anenvironment in which coexist the existing LTE-L service and LAA service.

In the overlay model, a macro base station may perform wirelesscommunication with an X UE and an X′ UE in a macro area (32) by using alicensed carrier and be connected with multiple radio remote heads(RRHs) through an X2 interface. Each RRH may perform wirelesscommunication with an X UE or an X′ UE in a predetermined area (31) byusing an unlicensed carrier. The frequency bands of the macro basestation and the RRH are different from each other not to interfere witheach other, but data needs to be rapidly exchanged between the macrobase station and the RRH through the X2 interface in order to use theLAA service as an auxiliary downlink channel of the LTE-L servicethrough the carrier aggregation.

In the co-located model, a pico/femto base station may perform thewireless communication with a Y UE by using both the licensed carrierand the unlicensed carrier. However, it may be limited that thepico/femto base station uses both the LTE-L service and the LAA serviceto downlink transmission. A coverage (33) of the LTE-L service and acoverage (34) of the LAA service may be different according to thefrequency band, transmission power, and the like.

When LTE communication is performed in the unlicensed band, conventionalequipments (e.g., wireless LAN (Wi-Fi) equipments) which performcommunication in the corresponding unlicensed band may not demodulate anLAA message or data. Therefore, conventional equipments determine theLAA message or data as a kind of energy to perform an interferenceavoidance operation by an energy detection technique. That is, whenenergy corresponding to the LAA message or data is lower than −62 dBm orcertain energy detection (ED) threshold value, the wireless LANequipments may perform communication by disregarding the correspondingmessage or data. As a result, that user equipment which performs the LTEcommunication in the unlicensed band may be frequently interfered by thewireless LAN equipments.

Therefore, a specific frequency band needs to be allocated or reservedfor a specific time in order to effectively implement an LAAtechnology/service. However, since peripheral equipments which performcommunication through the unlicensed band attempt access based on theenergy detection technique, there is a problem in that an efficient LAAservice is difficult. Therefore, a research into a coexistence schemewith the conventional unlicensed band device and a scheme forefficiently sharing a radio channel needs to be preferentially made inorder to settle the LAA technology. That is, a robust coexistencemechanism in which the LAA device does not influence the conventionalunlicensed band device needs to be developed.

FIG. 14 illustrates a conventional communication scheme (e.g., wirelessLAN) operating in an unlicensed band. Since most devices that operate inthe unlicensed band operate based on listen-before-talk (LBT), a clearchannel assessment (CCA) technique that senses a channel before datatransmission is performed.

Referring to FIG. 14, a wireless LAN device (e.g., AP or STA) checkswhether the channel is busy by performing carrier sensing beforetransmitting data. When a predetermined strength or more of radio signalis sensed in a channel to transmit data, it is determined that thecorresponding channel is busy and the wireless LAN device delays theaccess to the corresponding channel. Such a process is referred to asclear channel evaluation and a signal level to decide whether the signalis sensed is referred to as a CCA threshold. Meanwhile, when the radiosignal is not sensed in the corresponding channel or a radio signalhaving a strength smaller than the CCA threshold is sensed, it isdetermined that the channel is idle.

When it is determined that the channel is idle, a terminal having datato be transmitted performs a backoff procedure after a defer duration(e.g., arbitration interframe space (AIFS), PCF IFS (PIFS), or thelike). The defer duration means a minimum time when the terminal needsto wait after the channel is idle. The backoff procedure allows theterminal to further wait for a predetermined time after the deferduration. For example, the terminal stands by while decreasing a slottime for slot times corresponding to a random number allocated to theterminal in the contention window (CW) during the channel is idle, and aterminal that completely exhausts the slot time may attempt to accessthe corresponding channel.

When the terminal successfully accesses the channel, the terminal maytransmit data through the channel. When the data is successfullytransmitted, a CW size (CWS) is reset to an initial value (CWmin). Onthe contrary, when the data is unsuccessfully transmitted, the CWSincreases twice. As a result, the terminal is allocated with a newrandom number within a range which is twice larger than a previousrandom number range to perform the backoff procedure in a next CW. Inthe wireless LAN, only an ACK is defined as receiving responseinformation to the data transmission. Therefore, when the ACK isreceived with respect to the data transmission, the CWS is reset to theinitial value and when feed-back information is not received withrespect to the data transmission, the CWS increases twice.

As described above, since most communications in the unlicensed band inthe related art operate based on the LBT, the LTE also considers the LBTin the LAA for coexistence with the conventional device. In detail, inthe LTE, the channel access method on the unlicensed band may be dividedinto 4 following categories according to the presence/an applicationscheme of the LBT.

-   -   Category 1: No LBT        -   An LBT procedure by a Tx entity is not performed.    -   Category 2: LBT without random backoff        -   A time interval in which the channel needs to be sensed in            an idle state before the Tx entity performs a transmission            on the channel is decided. The random backoff is not            performed.    -   Category 3: LBT with random backoff with a CW of fixed size        -   LBT method that performs random backoff by using a CW of a            fixed size. The Tx entity has a random number N in the CW            and the CW size is defined by a minimum/maximum value of N.            The CW size is fixed. The random number N is used to decide            the time interval in which the channel needs to be sensed in            an idle state before the Tx entity performs a transmission            on the channel.    -   Category 4: LBT with random backoff with a CW of variable size        -   LBT method that performs the random backoff by using a CW of            a variable size. The Tx entity has the random number N in            the CW and the CW size is defined by the minimum/maximum            value of N. The Tx entity may change the CW size at the time            of generating the random number N. The random number N is            used to decide the time interval in which the channel needs            to be sensed in an idle state before the Tx entity performs            a transmission on the channel.

FIGS. 15 and 16 illustrate a DL transmission process based on a category4 LBT. The category 4 LBT may be used to ensure fair channel access withWi-Fi. Referring to FIGS. 15 and 16, the LBT process includes InitialCCA (ICCA) and Extended CCA (ECCA). That is, it is determined whetherthe channel is idle through the ICCA, and data transmission is performedafter the ICCA period. If the interference signal is detected and datatransmission fails, a data transmission time point may be obtainedthrough a defer duration+backoff counter after setting a random backoffcounter.

Referring to FIG. 15, the signal transmission process may be performedas follows.

Initial CCA

-   -   S202: The base station verifies that the channel is idle.    -   S204: The base station verifies whether the signal transmission        is required. When the signal transmission is not required, the        process returns to S202 and when the signal transmission is        required, the process proceeds to S206.    -   S206: The base station verifies whether the channel is idle for        an ICCA defer duration (BCCA). The ICCA defer duration is        configurable. As an implementation example, the ICCA defer        duration may be constituted by an interval of 16 vs and n        consecutive CCA slots. Herein, n may be a positive integer and        one CCA slot duration may be 9 vs. The number of CCA slots may        be configured differently according to a QoS class. The ICCA        defer duration may be set to an appropriate value by considering        a defer duration (e.g., DIFS or AIFS) of Wi-Fi. For example, the        ICCA defer duration may be 34 us. When the channel is idle for        the ICCA defer duration, the base station may perform the signal        transmitting process (S208). When it is determined that the        channel is busy during the ICCA defer duration, the process        proceeds to S212 (ECCA).    -   S208: The base station may perform the signal transmitting        process. When the signal transmission is not performed, the        process proceeds to S202 (ICCA) and when the signal transmission        is performed, the process proceeds to S210. Even in the case        where a backoff counter N reaches 0 in S218 and S208 is        performed, when the signal transmission is not performed, the        process proceeds to S202 (ICCA) and when the signal transmission        is performed, the process proceeds to S210.    -   S210: When additional signal transmission is not required, the        process proceeds to S202 (ICCA) and when the additional signal        transmission is required, the process proceeds to S212 (ECCA).

Extended CCA

-   -   S212: The base station generates the random number N in the CW.        N is used as a counter during the backoff process and generated        from [0, q−1]. The CW may be constituted by q ECCA slots and an        ECCA slot size may be 9 vs or 10 vs. The CW size (CWS) may be        defined as q and be variable in S214. Thereafter, the base        station proceeds to S216.    -   S214: The base station may update CWS. CWS q may be updated to a        value between X and Y. The X and Y values are configurable        parameters. The CWS update/adjustment may be performed each time        N is generated (dynamic back-off) or semi-static (semi-static        back-off) at certain time intervals. The CWS may be        updated/adjusted based on exponential back-off or binary        back-off. That is, the CWS may be updated/adjusted to a power of        2 or a multiple of 2. With respect to the PDSCH transmission,        the CWS may be updated/adjusted based on the terminal's        feedback/report (e.g., HARQ ACK/NACK) or updated/adjusted based        on the base station sensing.    -   S216: The base station determines that the channel is idle        during the ECCA defer duration (DeCCA). The ECCA defer duration        is configurable. As an embodiment, the ECCA defer duration may        be composed of a 16 μs section and n consecutive CCA slots.        Herein, n is a positive integer and one CCA slot duration may be        9 μs. The number of CCA slots may be set differently according        to the QoS class. The ECCA defer duration may be set to an        appropriate value by considering the defer duration of Wi-Fi        (e.g., DIFS and AIFS). For example, the ECCA defer duration may        be 34 us. If the channel is idle during the ECCA defer duration,        the base station proceeds to S218. If the channel is determined        to be busy during the ECCA defer duration, the base station        repeats S216.    -   S218: The base station checks if N is 0. If N is 0, the base        station may perform a signal transmission process (S208). In        this case (i.e., N=0), the base station may continue the ECCA        procedure by performing CCA checking during at least one slot        without performing the transmission immediately. If N is not 0        (i.e., N>0), the process proceeds to S220.    -   S220: The base station senses the channel for one ECCA slot        duration T. The ECCA slot size may be 9 μs or 10 μs, and the        actual sensing time may be at least 4 μs.    -   S222: If it is determined that the channel is idle, the process        proceeds to S224. If it is determined that the channel is busy,        the process returns to S216. That is, one ECCA defer duration is        reapplied after the channel is idle, and N does not count down        during the ECCA defer duration.    -   S224: Decrement N by 1 (ECCA countdown).

FIG. 16 is substantially the same as/similar to the transmission processof FIG. 15 and differs according to the implementation method.Therefore, the details may refer to the contents of FIG. 15.

Initial CCA

-   -   S302: The base station checks whether signal transmission is        needed. If no signal transmission is required, S302 is repeated,        and if signal transmission is required, the process proceeds to        S304.    -   S304: The base station checks if the slot is idle. If the slot        is idle, the process proceeds to S306. If the slot is busy, the        process proceeds to S312 (ECCA). The slot may correspond to the        CCA slot in FIG. 15.    -   S306: The base station checks that the channel is idle during        the defer duration D. D may correspond to the ICCA defer        duration in FIG. 15. If the channel is idle during the defer        duration, the base station may perform the signal transmission        process (S308). If it is determined that the channel is busy        during the defer duration, the process proceeds to S304.    -   S308: The base station may perform the signal transmission        process if necessary.    -   S310: If there is no signal transmission, the process proceeds        to S302 (ICCA), and if there is a signal transmission, the        process proceeds to S312 (ECCA). Even through the back-off        counter N reaches 0 in S318 and S308 is performed, if there is        no signal transmission, the process proceeds to S302 (ICCA) and        if there is signal transmission, the process proceeds to S312        (ECCA).

Extended CCA

-   -   S312: The base station generates a random number N in the CW. N        is used as a counter in the back-off process and is generated        from [0, q−1]. The CW size CWS is defined by q and may be varied        in S314. Thereafter, the base station proceeds to S316.    -   S314: The base station may update the CWS. CWS q may be updated        to a value between X and Y. The X and Y values are configurable        parameters. The CWS update/adjustment may be performed each time        N is generated (dynamic back-off) or semi-static (semi-static        back-off) at certain time intervals. The CWS may be        updated/adjusted based on exponential back-off or binary        back-off. That is, the CWS may be updated/adjusted to a power of        2 or a multiple of 2. With respect to the PDSCH transmission,        the CWS may be updated/adjusted based on the user equipment's        feedback/report (e.g., HARQ ACK/NACK) or updated/adjusted based        on the base station sensing.    -   S316: The base station checks that the channel is idle during        the defer duration D. D may correspond to the ECCA defer        duration in FIG. 15. D in S306 and S316 may be the same. If the        channel is idle during the defer duration, the base station        proceeds to S318. If the channel is determined to be busy during        the defer duration, the base station repeats S316.    -   S318: The base station checks if N is 0. If N is 0, the base        station may perform a signal transmission process (S308). In        this case (N=0), the base station may continue the ECCA        procedure by performing CCA checking during at least one slot        without performing the transmission immediately. If N is not 0        (i.e., N>0), the process proceeds to S320.    -   S320: The base station selects one of an operation of        decrementing N by 1 (ECCA countdown) and an operation of not        decrementing N (self-deferral). The self-deferral operation may        be performed according to the implementation/selection of the        base station. At the self-deferral time, the base station does        not perform sensing for energy detection and does not perform        ECCA countdown.    -   S322: The base station may select one of an operation not to        perform sensing for energy detection and an energy detection        operation. If sensing for energy detection is not performed, the        process proceeds to S324. When the energy detection operation is        performed, if the energy level is lower than the energy        detection threshold value (i.e., idle), the process proceeds to        S324. If the energy level exceeds the energy detection threshold        value (i.e., busy), the process returns to S316. That is, one        defer duration is reapplied after the channel is idle, and N        does not count down during the defer duration.    -   S324: The process proceeds to S318.

The channel access procedure described with reference to FIGS. 15 and 16may be used not only for DL transmission but also for UL transmission.Therefore, the base station as well as the user equipment may access thechannel according to the channel access procedure described withreference to FIG. 15 and FIG. 16. In the channel access proceduredescribed with reference to FIG. 15 and FIG. 16, the wirelesscommunication device waits for a slot duration by a random number inorder to disperse access time points of various wireless communicationdevices that perform channel access. Therefore, the probability ofselecting one of the values in the above-described CWS is uniform. Inaddition, for the purpose of access distribution, the wirelesscommunication device should wait for another time according to theobtained random number.

As described above, the wireless communication device determines whetherthe channel is idle during the defer duration. After the defer duration,the wireless communication device waits based on the counter value Ndetermined based on the random number and the slot duration. At thistime, the base station may start traffic transmission when the countervalue N is 0. In a specific embodiment, the traffic may be a datachannel. Specifically, the data channel may be either a PDSCH or aPUSCH. In yet another specific embodiment, the traffic may be a controlchannel. At this time, the control channel may be a PDCCH or an EPDCCH.The wireless communication device sets the counter value N to berandomly selected for access distribution and determines whether thechannel to be accessed during a slot duration is idle according to thecorresponding counter value. For convenience of explanation, thiscounter value setting procedure is referred to as a random counter valuesetting procedure.

Specifically, the wireless communication device senses whether thechannel is idle during the defer duration. When the channel is idleduring the defer duration, the wireless communication device may set thecounter value according to the following procedure.

1) The wireless communication device sets counter (N)=Ninit. Ninit is arandom number uniformly distributed within 0 and CW_(p).

2) When N>0 and the wireless communication device determines to decreaseN, set N=N−1.

3) Senses the channel during one additional slot duration, and when thechannel is idle during that one slot duration, the wirelesscommunication device goes to step 4), otherwise goes to step 5).

4) When N=0, the wireless communication device stops the counter valuesetting procedure. When not N=0, the wireless communication device goesto step 2).

5) The wireless communication device senses the channel during oneadditional defer duration.

6) When the channel is idle during a plurality of slot durations thatinclude one additional defer duration, the wireless communication devicegoes to step 2), and when the channel is not idle during that oneadditional defer duration, the wireless communication device goes tostep 5).

When the wireless communication terminal fails to transmit traffic onthe channel to be accessed in step 4) in the above-described procedure,the wireless communication terminal may transmit traffic when thechannel is idle during one additional defer duration. In addition, whenthe wireless communication device stops the counter value settingprocedure, the wireless communication device starts the traffictransmission.

When the traffic includes a data channel, the defer duration may be setaccording to the channel access priority class of the traffic that thedata channel is included in. At this time, the channel access priorityclass may be a channel access priority class. Also, the defer durationmay be composed of 16 us (Tf) and m_(p) number of slot durations. Atthis time, each slot duration Tsl may be 9 us. Tf includes one idle slotduration Tsl. Also, the m_(p) value may be set according to the channelaccess priority class as shown in Table 2 below.

TABLE 2 Channel Access Priority Class allowed (p) m_(p) CW_(min,p)CW_(max,p) T_(mcot.p) CW_(p) sizes 1 1 3 7 2 ms {3, 7} 2 1 7 15 3 ms {7,15} 3 3 15 63 8 or 10 ms {15, 31, 63} 4 7 15 1023 8 or 10 ms {15, 31,63, 127, 255, 511, 1023}

In addition, the wireless communication device may also set a range ofCW values according to the channel access priority class. Specifically,the wireless communication device may set the range of the CW values tosatisfy CW_(min,p)≤CW_(p)≤CW_(max,p). At this time, the value ofCW_(min,p) and the value of CW_(max,p) may be determined according tothe channel access priority class as shown in Table 2 described above.Also, the wireless communication device may set the value of CW_(min,p)and the value of CW_(max,p) in step 1) of the counter value settingprocedure. During channel access, the base station may adjust the CWvalue as described above.

Also, the maximum transmission duration T__(mcot,p) (maximum channeloccupancy time (MCOT)) that may be used in one transmission through achannel included in the unlicensed band may be determined according tothe channel access priority of the transmitted data. Specifically, itmay be determined as shown in Table 2 above. Accordingly, the wirelesscommunication device should not maintain a transmission continuouslymore than a time T_mcot,p. In the unlicensed band, since it is afrequency band accessed by several wireless communication devicesthrough contention procedures, it is not preferable that any one of thewireless communication devices continuously use the frequency band for apredetermined time or more. In Table 2, when the value of the channelaccess priority class is p=3 or p=4, in a long term, the unlicensed bandis used according to the rule, and there is no wireless communicationdevice using other technology, the wireless communication device may setto T__(mcot,p)=10 ms. Otherwise, the wireless communication device mayset to T__(mcot,p)=8 ms.

Also, the wireless communication device determines whether the channelis idle based on an energy detection (ED) threshold value. Specifically,the wireless communication device may determine that the channel is idlewhen the energy detected by the channel is smaller than the thresholdvalue. At this time, the ED threshold value may vary depending onwhether or not a wireless communication device using other technologycoexists. In addition, the ED threshold may vary depending on thecountry and region. Specifically, the ED threshold value may bedetermined as shown in Table 3 below.

TABLE 3 Case ED adaptation rule Note Case 1: Coexistance with othertechnologies $X\text{?}\mspace{14mu}\max\;\text{?}\begin{matrix}{{- 72}\mspace{14mu}{dBm}\mspace{14mu}\left( {20\mspace{14mu}{MHz}} \right)\text{?}} \\{\min\left\{ \begin{matrix}\text{?} \\\begin{matrix}\text{?} & \text{?} & \begin{pmatrix}\text{?} & \text{?}\end{pmatrix}\end{matrix}\end{matrix} \right.}\end{matrix}\text{?}$ T_(A) = 10 dB for fx(s) including PDSCH; T_(A) = 5dB for fx(s) including DRS transmission(s) and not including PDSCH-P_(H) = 23 dB -P_(TX) is the set Max eNB output power in dBm for thecarrier Case 2: Absence of Wi-Fi (e.g: by level of regulation)${X\text{?}}\; = \;{\min\begin{Bmatrix}{T_{\max} + {10\mspace{14mu}{{dB}.}}} \\\text{?}\end{Bmatrix}}$ Xr [dBm] is MAX ED threshold defined by regulationOtherwise ?indicates text missing or illegible when filed

In this case, the value of T__(max) in Table 3 may be determined asshown in the following equation.

T _(max) (dBm)=10·log 10(3.16228·10⁻⁸ (mW/MHz)·BW (114 Hz))

The wireless communication device may perform transmission through aplurality of carriers. Thus, the embodiments described above may be usedequally when a wireless communication device accesses a channel on anyone carrier as well as through a plurality of carriers. At this time,channel access methods for a plurality of carriers may be distinguishedas follows. When the wireless communication device performs the channelaccess procedure independently from each of a plurality of carriers, thecorresponding channel access may be classified as Type A. In this case,when the wireless communication device obtains a random numberindependently for each carrier, the corresponding channel access may beclassified as Type A1. Also, when one random number is obtained and usedbased on the largest CWS among the CWS corresponding to each carrier,the corresponding channel access may be classified as Type A2. Inaddition, when a wireless communication device accesses a channel on aplurality of carriers based on the channel access procedure for any onecarrier, the corresponding channel access may be classified as Type B.

When a wireless communication device accesses a channel on a pluralityof carriers according to the classification described above, thewireless communication device may not be able to start transmissionssimultaneously on a plurality of carriers. This is because channelstates corresponding to each of a plurality of carriers may be differentfrom each other and channel access parameters corresponding to each of aplurality of carriers, for example, defer duration may be different. Atthis time, due to the RF leakage occurring from the channel or thecarrier which starts transmission relatively first, the wirelesscommunication device may not be able to transmit signals on the channelor carrier that starts transmission at a relatively later time.

Therefore, the wireless communication device may perform an operationfor starting transmission simultaneously on a plurality of carriers inthe counter value setting procedure described above. Specifically, inthe counter value setting procedure described above, the wirelesscommunication device may selectively subtract 1 from the counter value.Through this, the wireless communication device may delay the start oftransmission on any one channel. As described above, this may bereferred to as self-deferral.

FIG. 17 shows a resource used by a base station after an LBT procedurein an unlicensed band according to an embodiment of the presentinvention.

In a cellular wireless communication system, radio resources may beallocated in units of a subframe. In this case, the base station and theUE access the radio resource based on the subframe boundary. Asdescribed above, when the base station or a user equipment accesses theunlicensed band, it is required to perform a contention procedure unlikethe licensed band. Specifically, the base station or the user equipmentmay perform an LBT procedure or a channel sensing procedure to accessthe unlicensed band.

Specifically, as in the embodiment of FIG. 17, a base station or a userequipment may transmit a PCell in a frequency band (e.g., a licensedband) in which the contention procedure is not performed, and transmitan SCell in an unlicensed band. In addition, the base station or userequipment may obtain transmission opportunities through the LBTprocedure in an SCell. In this case, the start of the transmissionopportunity on the SCell obtained by the base station or the userequipment may not match the boundaries of subframes as shown in FIG. 17.If the base station or user equipment waits after the contentionprocedure to access the channel based on the subframe boundaries, thebase station or user equipment may lose the transmission opportunityobtained through the contention procedure to other wirelesscommunication terminals.

Therefore, the base station or the user equipment is required toschedule the transmission time point of the data channel and the controlchannel through a method different from that used in the licensed band.Specifically, the base station or the user equipment may access radioresources regardless of the subframe boundaries in the unlicensed band.In a specific embodiment, the base station or user equipment may starttransmitting and receiving at any time point within the subframe in theunlicensed band. In this case, when the base station or the userequipment performs transmission during a time interval shorter than onesubframe, the corresponding time interval is referred to as a partialsubframe. In the embodiment of FIG. 17, the base station or the userequipment starts transmission in the SCell from the middle of the timeinterval corresponding to the n-th subframe Subframe n of the PCell.

Also, in the case of the unlicensed band, the maximum time that thewireless communication device may occupy the wireless resources may belimited. Therefore, the base station or user equipment may transmitpartial subframes at the end of transmission. In the embodiment of FIG.17, the base station or the user equipment ends the transmission in theSCell in the middle of the time interval corresponding to the (n+4)-thsubframe Subframe n+4 of the PCell.

In addition, the base station or the user equipment may transmit asignal to occupy radio resources before starting transmission. In thiscase, the signal for occupying the radio resource may be at least one ofan initial signal indicating the start of transmission, a reservationsignal including no information, an LAA preamble, and DRS. In this case,DRS may be Rel-12 DRS, or may be a combination of PSS, SSS, CRS, CSI-RSor a corresponding subset. Also, the signal for occupying the radioresource may be for matching the OFDM symbol unit (granularity) of thesignal transmitted from the base station or the user equipment.

The operation of the base station and the user equipment in theunlicensed band will be described in detail with reference to FIGS. 18to 23. In particular, an embodiment in which the base station transmitsa physical channel to the user equipment in the unlicensed band will bedescribed with reference to FIGS. 18 to 23. Meanwhile, the base stationin the specification may indicate at least one of a Transmission Point(TP), an Access Point (AP), and a Radio Remote Host (RRH).

FIG. 18 shows a method of a base station to transmit a control channelfor scheduling partial subframes after an LBT procedure in an unlicensedband according to an embodiment of the present invention. Specifically,FIG. 18 shows that the base station transmits one partial subframe atthe start of transmission, transmits three general subframes, andtransmits one partial subframe again after transmitting three generalsubframes.

The base station may transmit a control channel at each subframetransmitting data. Specifically, the base station may transmit PDCCH andEPDCCH for each subframe transmitting the PDSCH. In this case, thecontrol channel may only schedule data transmitted in the same carrieras the carrier in which the control channel is transmitted. For example,the base station may transmit the self-carrier scheduling controlchannel as described above. In yet another embodiment, the controlchannel may also schedule data transmitted in a carrier different fromthe carrier in which the control channel is transmitted. For example,the base station may transmit a control channel for cross-carrierscheduling as described above. When the base station transmits data andcontrol channels for scheduling data in the licensed band, the basestation transmits control channels from the beginning of the subframe.However, when accessing a channel of a frequency band through acontention procedure like an unlicensed band, a base station maytransmit partial subframes. When a base station transmits data through apartial subframe, it is a matter of how to transmit a control channelfor scheduling data to be transmitted through the partial subframe bythe base station.

A base station according to an embodiment of the present invention maytransmit, through a partial subframe, a control channel for schedulingdata transmitted through the partial subframe. Specifically, the basestation may transmit a control channel for scheduling data transmittedthrough the partial subframe before data transmission through thepartial subframe. In this case, the control channel may be at least oneof a PDCCH and an EPDCCH. For example, at the start of transmission, thebase station may transmit a PDSCH after transmitting a preamble in thepartial subframe and PDCCH for scheduling PDSCH, as in the embodiment ofFIG. 18(a). At the end of the transmission, the base station maytransmit the PDSCH after transmitting the PDCCH for scheduling the PDSCHin the partial subframe as in the embodiment of FIG. 18(a). Also, at thestart of transmission, the base station may transmit a preamble in thepartial subframe as in the embodiment of FIG. 18 (b) and starttransmission of E-PDCCH and PDSCH for scheduling PDSCH. At the end ofthe transmission, the base station may simultaneously transmit E-PDCCHand PDSCH for scheduling PDSCH in the partial subframe as in theembodiment of FIG. 18(b).

In another embodiment, the base station may transmit a control channelfor scheduling data transmitted through a subframe next to a partialsubframe or a subframe before the partial subframe. In this case, thebase station does not transmit the control channel through the partialsubframe. In this case, the control channel may be at least one of aPDCCH and an EPDCCH. In addition, the control channel may include anindicator indicating that data scheduled by the control channel istransmitted through the partial subframe. The DCI included in the PDCCHand the EPDCCH may include an indicator indicating that data scheduledby the PDCCH and the EPDCCH is transmitted through the partial subframe.For example, after transmitting a preamble in a partial subframe andtransmitting a PDSCH, as in the embodiment of FIG. 18(c), at the startof transmission, the base station may transmit the PDSCH transmitted inthe partial subframe and the PDCCH for scheduling the PDSCH transmittedthrough the corresponding subframe in the next subframe of the partialsubframe. At the end of the transmission, the base station may transmitthe PDSCH transmitted in the partial subframe in the previous subframeof the partial subframe and the PDCCH for scheduling the PDSCHtransmitted in the corresponding subframe, as in the embodiment of FIG.18(c). In addition, after transmitting a preamble in a partial subframeand transmitting a PDSCH, as in the embodiment of FIG. 18(d), at thestart of transmission, the base station may transmit the PDSCHtransmitted in the partial subframe and the E-PDCCH for scheduling thePDSCH transmitted through the corresponding subframe in the nextsubframe of the partial subframe. At the end of the transmission, thebase station may transmit the PDSCH transmitted in the partial subframein the previous subframe of the partial subframe and the E-PDCCH forscheduling the PDSCH transmitted in the corresponding subframe, as inthe embodiment of FIG. 18(d).

As mentioned above, the base station may transmit a reservation signalor an initial signal before partial subframe transmission.

In the embodiment described above, the base station treats the partialsubframe as a separate subframe. In another embodiment, the base stationmay treat the partial subframe and the other subframe as one subframehaving a TTI value larger than the TTI value of a general subframe. Forconvenience of explanation, a subframe having a TTI value larger than aTTI value of a general subframe is referred to as a super subframe. Inaddition, a subframe having a general TTI value for distinguishing fromthe super subframe is referred to as a general subframe. A method of abase station to transmit the super subframe will be described withreference to FIG. 19.

FIG. 19 shows a method of a base station to transmit a control channelfor scheduling the super subframes after an LBT procedure in anunlicensed band according to an embodiment of the present invention.Specifically, FIG. 19 shows that the base station transmits one supersubframe at the start of transmission, and then transmits one supersubframe again after transmitting one general subframe.

A base station according to an embodiment of the present invention maytransmit a control channel for scheduling data transmitted through apartial subframe, through a partial subframe. Specifically, the basestation may transmit a control channel for scheduling data transmittedthrough a super subframe before data transmission through a supersubframe. In this case, the control channel may be at least one of aPDCCH and an EPDCCH. For example, at the start of transmission, the basestation may transmit a PDSCH after transmitting a preamble in a supersubframe and a PDCCH for scheduling a PDSCH transmitted in a supersubframe as in the embodiment of FIG. 19(a). At the end of thetransmission, the base station may transmit the PDSCH after transmittingthe PDCCH for scheduling the PDSCH in the super subframe as in theembodiment of FIG. 19(a). Also, at the start of transmission, the basestation may transmit a preamble in a super subframe as in the embodimentof FIG. 19 (b) and start transmission of E-PDCCH and PDSCH forscheduling PDSCH. At the end of the transmission, the base station maysimultaneously transmit E-PDCCH and PDSCH for scheduling PDSCH in asuper subframe as in the embodiment of FIG. 19(b). In this case, thesize of the E-PDCCH may vary according to the data scheduled by theE-PDCCH.

In another specific embodiment, the base station may transmit a controlchannel for scheduling data transmitted through a super subframe basedon a boundary of a general subframe included in the super subframe.Specifically, the base station may transmit a control channel forscheduling data transmitted through a super subframe at a starting timepoint of a general subframe included in the super subframe.

For example, at the start of transmission, the base station may transmita preamble in the super subframe and start PDSCH transmission as in theembodiment of FIG. 19(c). In this case, the base station may transmit aPDCCH for scheduling the PDSCH transmitted through the super subframe atthe starting time point of the general subframe included in the supersubframe. At the end of the transmission, the base station may transmitthe PDSCH after transmitting the PDCCH for scheduling the PDSCHtransmitted in the super subframe as in the embodiment of FIG. 19(c). Inaddition, at the start of transmission, the base station may transmit apreamble in the super subframe and start PDSCH transmission as in theembodiment of FIG. 19(d). In this case, the base station may transmit anE-PDCCH for scheduling the PDSCH transmitted through the super subframefrom the starting time point of the general subframe included in thesuper subframe. In this case, the size of the E-PDCCH may vary accordingto the data scheduled by the E-PDCCH. At the end of the transmission,the base station may simultaneously transmit E-PDCCH and PDSCH forscheduling PDSCH transmitted in the super subframe as in the embodimentof FIG. 19(d).

The control channel described above may include an indicator indicatingwhether data to be scheduled by the control channel is transmittedthrough the super subframe or a general subframe. Specifically, the DCIincluded in the PDCCH or the E-PDCCH may include an indicator indicatingwhether the data scheduled by the PDCCH or the E-PDCCH is transmittedthrough the super subframe or the general subframe.

Through FIGS. 18 to 19, an embodiment is described in which a basestation transmits a control channel in an unlicensed band on the basisof a boundary of a general subframe or a starting time point oftransmission. A base station may transmit control channels at varioustime points within a subframe. An embodiment in which a base stationtransmits control channels at various time points within a subframe willbe described with reference to FIGS. 20 to 22.

FIG. 20 shows another method of a base station to transmit a controlchannel for scheduling the super subframes after an LBT procedure in anunlicensed band according to an embodiment of the present invention.

The base station may transmit a control channel for scheduling datatransmitted through the super subframe at the start of the transmissionof the super subframe. For example, the base station may transmit thecontrol channel at the start of the transmission of the super subframes2001 and 2021 as in the first embodiments 2011 and 2031 of FIG. 20(a)and FIG. 20(b). In this case, the user equipment may receive the controlchannel first, and end the data reception when the decoded controlchannel does not schedule the data corresponding to the user equipment.Also, the user equipment is not required to buffer the data transmittedto the other user equipment in advance. Therefore, at the start oftransmission of the super subframe, the base station may increase theoperation efficiency of the user equipment by transmitting a controlchannel for scheduling data transmitted through the super subframe.

As described above, the base station may access radio resources in theunlicensed band regardless of subframe boundaries. In a specificembodiment, the base station or user equipment may start transmission atany time point within the subframe in the unlicensed band. Therefore,when accessing the unlicensed band, the base station may transmit thesignal for occupying the above-mentioned radio resource first. In aspecific embodiment, the user equipment may monitor the signal foroccupying the radio resource. When the user equipment senses the signalfor occupying the radio resource, the user equipment may determine thatthe base station transmits data. Thus, by transmitting the signal foroccupying the radio resource, the base station may prevent anotherwireless communication user equipment from accessing radio communicationresources before transmitting the control channel and data. In addition,the base station may signal the user equipment that the base station isstarting data transmission. In addition, the base station may transmit asignal for occupying radio resources, thereby matching OFDM symbolunits.

Accordingly, the base station may transmit a signal for occupying radioresources before the super subframe transmission. In this case, the userequipment must perform blind decoding of the control channel includingcontrol information for each received OFDM symbol until receiving thecontrol channel.

The base station may transmit the control channel together from any oneof the OFDM symbols previously designated to transmit the referencesignal. In this case, as described above, the base station may transmita signal for occupying radio resources and transmit the super subframe.The base station may adjust the duration of the signal for occupying theradio resources to make the start of transmission of the super subframecorrespond to one of the OFDM symbols previously designated to transmitthe reference signal. Also, the reference signal may be a Cell SpecificReference Signal (CRS). Specifically, the reference signal may be CRSport 0 or CRS port 1. In addition, the index value of the OFDM symbol inwhich the CRS is transmitted may be at least one of 0, 4, 7, and 11.According to the operation of the base station, the user equipment mayreceive the control information by monitoring the reception of thecontrol channel from the OFDM symbol position previously designated totransmit the reference signal.

When the control channel is the E-PDCCH and the subframe boundaries ofPCell and SCell match to each other, based on PCell's OFDM symbol index,the base station may transmit the E-PDCCH in an OFDM symbol positionthat does not split the downlink demodulation reference signal (DMRS).For example, the base station may transmit the E-PDCCH in an OFDM symbolposition 2032 that does not split the DMRS, as in the second embodiment2022 of FIG. 20(b). The reason is that if the DMRS is split by theE-PDCCH, the user equipment may not use one DMRS port fordecoding/demodulating the E-PDCCH. Specifically, the base station maytransmit an E-PDCCH from an OFDM symbol that is not the sixth OFDMsymbol of the first slot of the subframe and the sixth OFDM symbol ofthe second slot based on the normal CP. That is, the base station maytransmit an E-PDCCH from any one OFDM symbol of the first OFDM symbol tothe fifth OFDM symbol in the first slot of the subframe and the firstOFDM symbol to the fifth OFDM symbol in the second slot, based on thenormal CP. Also, the base station may adjust the duration of the signalfor occupying the radio resources to transmit the E-PDCCH in an OFDMsymbol position that does not split the downlink DMRS while transmittingthe signal for occupying the above-described radio resource before thesuper subframe transmission. In this case, the user equipment maydemodulate/decode a signal including the E-PDCCH for a duration of ageneral subframe, and then determine whether to receive a PDSCH. Throughthis operation, the base station may improve the decoding/demodulationperformance of the signal including the E-PDCCH of the terminal.

In another embodiment, the base station may transmit a control channeland a reference signal together. Specifically, the base station maytransmit the reference signal together when transmitting the controlchannel. In yet another specific embodiment, the transmission of controlchannel may be started from an OFDM symbol designated to transmit thereference signal. The user equipment estimates a state of a controlchannel and a channel through which data is transmitted using areference signal, and receives the control channel and the data toperform demodulation/decoding by using the estimated channel state.Therefore, when the base station starts to transmit the control channelfrom the OFDM symbol designated to transmit the reference signal, theuser equipment may stably receive the control channel. In this case, thereference signal may be a CRS as in the above-described embodiment. Inaddition, the index value of the OFDM symbol in which the referencesignal is transmitted may be at least one of 0, 4, 7, and 11. The indexvalue of the OFDM symbol in which the CRS is transmitted may be apredetermined value. For example, the base station may transmit thecontrol channel at the positions 2002 and 2003 of the OFDM symbol inwhich the reference signal is transmitted as in the second and thirdembodiments 2012 and 2013 of FIG. 20(a).

In another embodiment, the base station may transmit a control channelin an OFDM symbol closest to a starting time point of transmission amonga plurality of OFDM symbol indexes in which a reference signal istransmitted. In this embodiment, the base station may first transmitdata scheduled by the control channel before transmitting the controlchannel. In another specific embodiment, the base station may adjust thelength of the signal occupying the radio resource, and transmit thecontrol channel before the data transmission scheduled by the controlchannel. In this case, the operation of the base station may be the sameas the operation of the base station in the concrete embodimentdescribed in the first embodiments 2011 and 2031 of FIGS. 20(a) and20(b).

In another embodiment, the base station may transmit a control channelbased on the boundary of the subframe. In this case, the boundary of thesubframe is the boundary of the normal subframe included in the supersubframe, not the super subframe. Specifically, the base station maytransmit the control channel at the starting time point of the subframe.For example, the base station may transmit a control channel at thestarting time points 2004 and 2023 of the subframe as in the fourthembodiment 2014 of FIG. 20(a) and the third embodiment 2033 of FIG.20(b). In this case, the base station may transmit data beforetransmitting the control channel for scheduling the data. Therefore, theuser equipment may buffer the data until receiving the control channel.

The control channel described with reference to FIG. 20 may be used forboth the above-described self-carrier scheduling and cross-carrierscheduling according to a specific embodiment. Further, in theembodiment described with reference to FIG. 20, the base station maytransmit the PCell in a frequency band that is accessible without acontention procedure, for example, a licensed band.

In the embodiment described with reference to FIGS. 17 to 20, theboundary of the subframe of SCell is aligned with the subframe boundaryof PCell. In this case, the base station had to transmit a partialsubframe or a super subframe in the unlicensed band SCell. In theexisting wireless communication system, it is assumed that resources areallocated and transmitted in units of subframes having a 1 ms length,for example. Therefore, when a base station and a user equipmenttransmit a partial subframe or a super subframe, the operations of thebase station and the user equipment may be complicated. To solve thisproblem, the base station may set the starting time point of thesubframe based on the time point at which transmission starts in theunlicensed band SCell. Through this, the base station may transmit anormal subframe at the start of transmission. This will be described inmore detail with reference to FIG. 21.

FIG. 21 shows a method of a base station to transmit a control channelfor scheduling a subframe having a different boundary from a boundary ofa subframe of a PCell, after performing an LBT procedure in anunlicensed band according to an embodiment of the present invention.

As described above, the base station may set the starting time point ofthe transmission of the SCell transmitted in the unlicensed band to thestarting time point of the SCell subframe. In this case, the time thatthe base station may occupy the radio resource may not be a multiple ofthe subframe length of the SCell. In this case, the base station maytransmit the partial subframe at the end of the transmission. When thebase station sets the starting time point of the transmission of theSCell transmitted in the unlicensed band to the starting time point ofthe SCell subframe, the base station may apply the embodiment describedwith reference to FIG. 20 based on the subframe boundary of the SCell.

Specifically, the base station may transmit a control channel forscheduling data to be transmitted through a subframe of SCell at thestart of subframe transmission of the SCell. For example, the basestation may transmit the control channel at the starts 2101 and 2121 ofthe transmission of the Scell subframes as in the first embodiments 2111and 2131 of FIG. 21(a) and FIG. 21(b). In this case, the user equipmentmay receive the control channel first, and end the data reception whenthe decoded control channel does not schedule the data corresponding tothe terminal. Also, the user equipment does not need to buffer the datatransmitted to the other user equipment in advance. Therefore, at thestart of transmission of the SCell subframe, the base station mayincrease the operation efficiency of the user equipment by transmittinga control channel for scheduling data transmitted through the SCellsubframe.

In this case, the base station may transmit a signal for occupying radioresources before the SCell subframe transmission. In this case, the userequipment must perform blind decoding of the control channel includingcontrol information for each received OFDM symbol until receiving thecontrol channel.

The base station may transmit the control channel together from any oneof the OFDM symbols previously designated to transmit the referencesignal. In this case, as described above, the base station may transmita signal for occupying radio resources and transmit the SCell subframe.The base station may adjust the duration of the signal for occupying theradio resources to make the start of transmission of the super subframecorrespond to one of the OFDM symbols previously designated to transmitthe reference signal. Also, the reference signal may be a CRS.Specifically, the reference signal may be CRS port 0 or CRS port 1. Inaddition, the index value of the OFDM symbol in which the CRS istransmitted may be at least one of 0, 4, 7, and 11. According to theoperation of the base station, the user equipment may receive thecontrol information by monitoring the reception of the control channelfrom the OFDM symbol position previously designated to transmit thereference signal.

When the control channel is an E-PDCCH, the base station may transmitthe E-PDCCH in an OFDM symbol position that does not split the downlinkdemodulation reference signal (DMRS) based on the OFDM symbol index ofthe PCell. For example, the base station may transmit the E-PDCCH in anOFDM symbol position 2132 that does not split the DMRS, as in the secondembodiment 2122 of FIG. 21(b). The reason is that if the DMRS is splitby the E-PDCCH, the user equipment may not use one DMRS port fordecoding/demodulating the E-PDCCH. Specifically, the base station maytransmit an E-PDCCH from an OFDM symbol that is not the sixth OFDMsymbol of the first slot of the subframe and the sixth OFDM symbol ofthe second slot based on the normal CP. That is, the base station maystart to transmit an E-PDCCH in any one OFDM symbol of the first OFDMsymbol to the fifth OFDM symbol in the first slot of the PCell subframeand the first OFDM symbol to the fifth OFDM symbol in the second slot,based on the normal CP. Through this operation, the base station mayimprove the decoding/demodulation performance of the signal includingthe E-PDCCH of the terminal.

In another embodiment, the base station may transmit a control channeland a reference signal together. Specifically, the base station maytransmit a reference signal together when transmitting a controlchannel. In yet another specific embodiment, the transmission of thecontrol channel may be started in an OFDM symbol position designated totransmit a reference signal. The user equipment estimates a state of acontrol channel and a channel through which data is transmitted using areference signal, and demodulates/decodes the control channel and thedata by using the estimated channel state. Therefore, when the basestation starts to transmit the control channel in the OFDM symbolposition in which the reference signal is transmitted, the userequipment may stably receive the control channel. In this case, thereference signal may be a CRS as in the above-described embodiment. Inaddition, the index value of the OFDM symbol in which the referencesignal is transmitted may be at least one of 0, 4, 7, and 11. The indexvalue of the OFDM symbol in which the CRS is transmitted may be apredetermined value. For example, the base station may transmit thecontrol channel at the positions 2112 and 2113 of the OFDM symbol inwhich the reference signal is transmitted as in the second and thirdembodiments 2102 and 2103 of FIG. 21(a).

In a specific embodiment, the base station may transmit a controlchannel in an OFDM symbol closest to a starting time point of thetransmission among a plurality of OFDM symbol indexes in which areference signal is transmitted. In this embodiment, the base stationmay first transmit data scheduled by the control channel beforetransmitting the control channel. In another specific embodiment, thebase station may adjust the length of the signal occupying the radioresource, and transmit the control channel before the data transmissionscheduled by the control channel. In this case, the operation of thebase station may be the same as the operation of the base station in theconcrete embodiment described in the first embodiments 2111 and 2131 ofFIGS. 21(a) and 21(b).

In another embodiment, the base station may transmit a control channelbased on the boundary of the PCell subframe. Specifically, the basestation may transmit the control channel in the SCell at the startingtime point of the PCell subframe. For example, the base station maytransmit a control channel in the SCell at the starting time points 2104and 2123 of the PCell subframe as in the fourth embodiments 2014 and2033 of FIG. 21(a) and FIG. 21(b). In this case, the base station maytransmit data before transmitting the control channel for scheduling thedata. Therefore, the user equipment may buffer the data until receivingthe control channel.

The control channel described with reference to FIG. 21 may be used forboth the above-described self-carrier scheduling and cross-carrierscheduling according to a specific embodiment. Further, in theembodiment described with reference to FIG. 21, the base station maytransmit the PCell in a frequency band that is accessible without acontention procedure, for example, a licensed band.

As in the above-described embodiment, the base station may treat partialsubframes as individual subframes in an SCell transmitted in anunlicensed band. In this case, a method of a base station to transmit acontrol channel will be described with reference to FIG. 22.

FIG. 22 shows another method of a base station to transmit a controlchannel for scheduling the partial subframes after an LBT procedure inan unlicensed band according to an embodiment of the present invention.

The base station may transmit a control channel for scheduling datatransmitted through the partial subframe at the start of thetransmission of the partial subframe. For example, the base station maytransmit the control channel at the start of the transmission of thepartial subframe 2211 and 2231 as in the first embodiment 2201 and 2221of FIG. 22(a) and FIG. 22(b). In this case, the user equipment mayreceive the control channel first, and end the data reception if thedecoded control channel does not schedule the data corresponding to theuser equipment. Also, the user equipment does not need to buffer thedata transmitted to the other user equipment in advance. Therefore, atthe start of transmission of the partial subframe, the base station mayincrease the operation efficiency of the user equipment by transmittinga control channel for scheduling data transmitted through the partialsubframe.

The base station may transmit a signal for occupying radio resourcesbefore the super subframe transmission. In this case, the user equipmentmust perform blind decoding of the control channel including controlinformation for each received OFDM symbol until receiving the controlchannel.

The base station may transmit a control channel including controlinformation from any one of the OFDM symbol positions previouslydesignated to transmit the reference signal. In this case, as describedabove, the base station may transmit a signal for occupying radioresources and transmit the partial subframe. The base station may adjustthe duration of the signal for occupying the radio resources so that thestart of transmission of the partial subframe corresponds to one of theOFDM symbol positions previously designated to transmit the referencesignal. Also, the reference signal may be a CRS. Specifically, thereference signal may be CRS port 0 or CRS port 1. In addition, the indexvalue of the OFDM symbol in which the CRS is transmitted may be at leastone of 0, 4, 7, and 11. According to the operation of the base station,the user equipment may receive the control information by monitoring thereception of the control channel from the OFDM symbol positionpreviously designated to transmit the reference signal.

When the control channel is the E-PDCCH and the subframe boundaries ofPCell and SCell match to each other, the base station may transmit,based on PCell's OFDM symbol index, the E-PDCCH in an OFDM symbolposition that does not split the downlink DMRS (demodulation referencesignal). For example, the base station may transmit the E-PDCCH in anOFDM symbol position 2222 that does not split the DMRS, as in the secondembodiment 2232 of FIG. 22(b). The reason is that if the DMRS is splitby the E-PDCCH, the user equipment may not use one DMRS port fordecoding/demodulating the E-PDCCH. Specifically, the base station maytransmit an E-PDCCH from an OFDM symbol that is not the sixth OFDMsymbol of the first slot of the subframe and the sixth OFDM symbol ofthe second slot based on the normal CP. That is, the base station maytransmit an E-PDCCH from any one OFDM symbol of the first OFDM symbol tothe fifth OFDM symbol in the first slot of the subframe and the firstOFDM symbol to the fifth OFDM symbol in the second slot, based on thenormal CP. Through this, the base station may improve thedecoding/demodulation performance of the signal including the E-PDCCH ofthe user equipment.

In another embodiment, the base station may transmit a control channeland a reference signal together. Specifically, the base station maytransmit a reference signal together when transmitting a controlchannel. In yet another specific embodiment, the control channel may betransmitted from an OFDM symbol designated to transmit a referencesignal. The user equipment estimates a state of a control channel and achannel through which data is transmitted using a reference signal, anddemodulates/decodes the control channel and the data by using theestimated channel state. Therefore, when the base station transmits thecontrol channel and the reference signal together, the user equipmentmay stably receive the control channel. In this case, the referencesignal may be a CRS as in the above-described embodiment. In addition,the index value of the OFDM symbol in which the reference signal istransmitted may be at least one of 0, 4, 7, and 11. The index value ofthe OFDM symbol in which the CRS is transmitted may be a predeterminedvalue. For example, the base station may transmit the control channel atthe positions 2212 and 2213 of the OFDM symbol in which the referencesignal is transmitted as in the second and third embodiments 2202 and2203 of FIG. 20(a).

In another embodiment, the base station may start to transmit a controlchannel in the OFDM symbol position closest to a starting time point ofthe transmission among a plurality of OFDM symbol indexes in which areference signal is transmitted. In this embodiment, the base stationmay first transmit data scheduled by the control channel beforetransmitting the control channel. In another specific embodiment, thebase station may adjust the length of the signal occupying the radioresource, and transmit the control channel before the data transmissionscheduled by the control channel. In this case, the operation of thebase station may be the same as the operation of the base station in theconcrete embodiment described in the first embodiments 2211 and 2231 ofFIGS. 22(a) and 22(b).

In another embodiment, the base station may transmit a control channelbased on the boundary of the subframe. In this case, the boundary of thesubframe is the boundary of the general subframe, not the partialsubframe. Specifically, the base station may transmit a control channelat a starting time point of a general subframe positioned after apartial subframe. For example, the base station may transmit a controlchannel at the starting time points 2204 and 2223 of a general subframepositioned next to a partial subframe, as in the fourth embodiments 2214and 2233 of FIGS. 22(a) and 22(b). In this case, the base station maytransmit data before transmitting the control channel for scheduling thedata. Therefore, the user equipment may buffer the data until receivingthe control channel.

The control channel described with reference to FIG. 22 may be used forboth the above-described self-carrier scheduling and cross-carrierscheduling according to a specific embodiment. Further, in theembodiment described with reference to FIG. 22, the base station maytransmit the PCell in a frequency band that is accessible without acontention procedure, for example, a licensed band.

The base station may use a different transmission method of the controlchannel of the partial subframe at the end of transmission in theembodiments described with reference to FIGS. 20 to 22 from thetransmission method of the control channel of the partial subframe atthe start of transmission. Specifically, the base station may apply thecontrol channel transmission method described with reference to FIG. 20to FIG. 22 differently to the partial subframe transmitted at the startof transmission and the partial subframe transmitted at the end oftransmission.

When a base station is to transmit a downlink burst composed of a singlesubframe or a plurality of subframes for downlink transmission in aspecific cell on an unlicensed band, channel access must be performedbefore the transmission of DL bursts consisting of DL channels. In thiscase, when the base station performs channel access with cat-4 LBT, thatis, random backoff, transmission of the DL channel may not be guaranteedat a specific subframe boundary. In this case, the user equipment maynot perform data transmission during at least one OFDM symbol and up toa subframe of 1 ms. In order to prevent such radio resource waste, thebase station may transmit a physical channel at the subframe boundary orthe starting time point of the second slot of the subframe. If the basestation still succeeds in the LBT at a different location within thesubframe, which is not the subframe boundary or is not prior to thestarting time point of the second slot of the subframe, there are somecases where data transmission may not be performed during at least oneOFDM symbol resource and up to seven OFDM symbol resources. In such anembodiment, the base station may not transmit all of the physicalchannels intended to be transmitted through DL transmission or may needto further transmit a meaningless signal.

When the base station starts DL transmission using a partial subframe,the base station may determine the ending position of the OFDM symbolincluded in the last subframe of the DL transmission based on thestarting position of the partial subframe. Specifically, when the basestation starts DL transmission using a partial subframe and fails tostart DL transmission at a specified time point, the base station maydetermine the ending position of the OFDM symbol included in the lastsubframe of the DL transmission based on the number of OFDM symbols usedfor the DL transmission. In relation to this, a method of the basestation to signal the starting time point of the DL transmission isdescribed when the base station can start DL transmission at a timepoint other than the subframe boundary. Furthermore, a method of thebase station to determine a DL transmission configuration is describedwhen the base station can start DL transmission at a time point otherthan the subframe boundary.

As described above, when the base station transmits a partial subframe,the base station may transmit a reference signal and a control channeltogether. In more detail, when the base station transmits a partialsubframe, the base station may transmit a control channel in an OFDMsymbol in which a reference signal is transmitted. In this case, thereference signal may be a CRS. In addition, the index value of the OFDMsymbol in which the reference signal is transmitted may be at least oneof 0, 4, 7, and 11. The control channel and the data channel may beallocated according to time division multiplexing (TDM). In this case,after transmitting the control channel for scheduling the data channel,the base station may transmit the data channel. Through this, the basestation may reduce the buffering burden on the data channel of the userequipment. The downlink pilot time slot (DwPTS) may have a duration ofany one of 3, 6, 9, 10, 11, and 12 OFDM symbols. In this case, when thebase station schedules for each subframe, the base station may determinethe duration of the DwPTS according to the starting time point of thetransmission of the partial subframe. In more detail, the base stationmay determine the duration of the DwPTS such that the time elapsed bythe duration of the DwPTS from the starting time point of thetransmission of the partial subframe does not cross the subframeboundary. For example, when starting DL transmission from an OFDM symbolhaving an OFDM symbol index of 4, the base station may transmit a datachannel using DwPTS having 10 OFDM symbols as a duration. In addition,when starting DL transmission from an OFDM symbol having an OFDM symbolindex of 11, the base station may transmit a data channel using DwPTShaving 3 OFDM symbols as a duration.

In addition, the base station may determine the configuration of the DLtransmission based on the capability of the user equipment. In moredetail, the base station may determine whether to transmit a partialsubframe when starting DL transmission based on the capability of theuser equipment.

In more detail, the base station may determine the starting time pointof the DL transmission based on the capability of the user equipment.According to a specific embodiment, when the user equipment may receiveDL transmission at the starting time point of the second slot of thesubframe and the subframe boundary, the base station may start DLtransmission at the starting time point of the second slot or thesubframe boundary. In addition, when the user equipment is capable ofreceiving the DL transmission from the OFDM symbol corresponding to theindex values 0, 4, 7, and 11 of the OFDM symbol, the base station maystart DL transmission in an OFDM symbol corresponding to any one ofindex values 0, 4, 7, and 11 of the OFDM symbol. In addition, when theuser equipment is capable of receiving the DL transmission at theboundary of the subframe, the base station may start the DL transmissionat the subframe boundary. In such embodiments, the base station mayindicate the starting time point of the DL transmission to the userequipment using RRC signaling. The user equipment may monitor the DLdata channel at a time point indicated by RRC signaling. Specifically,when the user equipment is capable of receiving DL transmission at thestarting time point of the second slot and the subframe boundary, theuser equipment may monitor the DL data channel at least one of thestarting time point of the second slot and the subframe boundary basedon the RRC signaling. In addition, when the user equipment is capable ofreceiving the DL transmission from the OFDM symbol corresponding to theindex values 0, 4, 7, and 11 of the OFDM symbol, the user equipment maymonitor the DL data channel at least one of the index values 0, 4, 7,and 11 of the OFDM symbol based on the RRC signaling.

The base station may transmit the last subframe of the DL transmissionas a partial subframe. In this case, the duration of the partialsubframe may correspond to any one of 3, 6, 9, 10, 11, and 12 OFDMsymbols, and the duration of the partial subframe may correspond to anyone of 4 and 5 OFDM symbols. In DL transmission, a base station maytransmit only one partial subframe. In this case, the partial subframeis not only the initial partial subframe but also the ending partialsubframe. When the partial subframe is not only the initial partialsubframe but also the ending partial subframe, the base station maytransmit a partial subframe having a duration of 4 or 5 OFDM symbols.Accordingly, the user equipment may receive a partial subframe having 4or 5 OFDM symbol durations. In more detail, the base station maydetermine the duration of the partial subframe such that at least one ofCRS port 0 and CRS port 1 is transmitted. In the above-describedembodiment, the base station may improve the channel estimationperformance of the user equipment by setting the duration of the partialsubframe to include two OFDM symbols including CRS port 0 and CRS port1.

FIG. 23 shows a UL transmission method of a user equipment according toan embodiment of the present invention. Specifically, the structure ofthe UL subframe and the ending position of the last subframe of the ULtransmission will be described with reference to FIGS. 23 to 31.

FIG. 23 shows an UL subframe structure transmitted by a user equipmentaccording to an embodiment of the present invention.

The user equipment may perform UL transmission using SC-FDMA. The basestation may schedule the UL transmission of the user equipment for eachsubframe. The user equipment may transmit 12 to 14 SC-FDMA symbols inone subframe according to the scheduling of the base station.Specifically, the user equipment may start UL transmission between anSC-FDMA symbol having an index of 0 in a subframe or an SC-FDMA symbolhaving an index of 1 in a subframe or an SC-FDMA symbol having an indexof 0 and an SC-FDMA symbol having an index of 1. In addition, the indexof the last SC-FDMA symbol of the subframe transmitted by the userequipment may be 13 or index 12 depending on whether Sounding ReferenceSignal (SRS) is transmitted. In addition, the base station may indicatean index of the last SC-FDMA symbol for UL data channel transmission ina subframe through which the user equipment performs UL data channeltransmission using a UL grant.

In relation to frequency bandwidth occupancy regulation applied to theunlicensed band, the base station may allocate a frequency band for ULtransmission so that the user equipment can use the entire channelfrequency band. In this case, as shown in FIG. 23, the user equipmentuses an interlaced structure configured to equally divide the totalnumber of RBs used in one carrier into 10 and have a 10 RB interval inthe frequency domain. For example, a user equipment can transmit oneinterlaced composed of at least 10 RBs based on a 20 MHz bandwidth. Inthis case, one interlaced is composed of 10 RBs having 10 RB intervalsin the frequency domain. A user equipment may perform UL transmission byreceiving a single or a plurality of interlaces from a base station. Theuser equipment may perform uplink transmission in units of 1 ms. In moredetail, the user equipment may utilize a system bandwidth as shown inFIG. 23. The user equipment receiving the UL grant from the base stationmay attempt channel access for UL transmission using type 1 channelaccess or type 2 channel access. In this case, the type 1 channel accessmay indicate a channel access based random backoff. In more detail, thetype 1 channel access may indicate a channel access method in which auser equipment obtains a random value in a contention window andaccesses the channel based on whether the channel is idle for a timeinterval determined based on the random value obtained by the userequipment. In more detail, the type 1 channel access may indicate achannel access method using the cat-4 LBT described above. In addition,the type 2 channel access may indicate a channel access method in whicha user equipment accesses a channel based on whether the channel is idlefor a predetermined time interval. In this case, the predetermined timesection may be 25 us. In more detail, the type 2 channel access mayindicate a channel access using the cat-2 LBT described above. When theuser equipment fails to access the channel while performing ULtransmission according to the RB unit and the time unit described above,transmission resources with 10 RBs and 1 ms duration can be wasted. Inorder to reduce such transmission resource waste, a method of variouslysetting a starting time point and an ending time point of ULtransmission of a user equipment may be used.

FIGS. 24 and 25 show that a user equipment is configured to receive astarting partial subframe of a UL transmission from a base station toperform a UL transmission to a base station according to an embodimentof the present invention.

Hereinafter, the transmitting the partial subframemay indicatetransmitting a physical channel in the partial subframe.

The user equipment may transmit the physical channel and the UL DM-RStogether. The base station may coherently demodulate the receivedphysical channel using UL DM-RS. Therefore, the user equipment maytransmit the partial subframe in consideration of the DM-RStransmission.

The user equipment may be configured by the base station to transmit apartial subframe including at least one UL DM-RS to the base station. Inthis case, the UL DM-RS may be a reference signal for demodulation ofthe data channel and the control channel transmitted through the UL. Inmore detail, the user equipment may start transmitting partial subframesto the base station at the slot boundary. In this case, the userequipment may transmit a partial subframe having a duration of 6 and 7SC-FDMA symbols. That is, when UL transmission that ends at the SC-FDMAsymbol index 12 is scheduled, the user equipment may transmit a partialsubframe having a duration of 6 SC-FDMA symbols at the second slotboundary of the subframe. Furthermore, when UL transmission that ends atthe SC-FDMA symbol index 13 is scheduled, the user equipment maytransmit a partial subframe having a duration of 7 SC-FDMA symbols atthe second slot boundary of the subframe. FIG. 24(a) shows an operationin which a user equipment starts partial subframe transmission for abase station at a slot boundary.

In another specific embodiment, the user equipment may starttransmission of the partial subframe for the base station from at leastone of the UL DM-RS transmission starting position as well as the slotboundary. In this case, the UL DM-RS may be a reference signal fordemodulation of the data channel and the control channel transmittedthrough the UL. In more detail, the user equipment may start partialsubframe transmission for the base station in the SC-FDMA symbol, whichis one of the SC-FDMA symbols transmitting the UL DM-RS having the index3 or 10, as well as the slot boundary. FIG. 24(b) shows an operation inwhich a user equipment starts partial subframe transmission for a basestation from a UL DM-RS transmission starting position as well as a slotboundary.

In another specific embodiment, the user equipment transmits a partialsubframe including at least one UL DM-RS to the base station regardlessof whether the transmission starting position of the partial subframe isa slot boundary or an SC-FDMA symbol position of the UL DM-RS. In thiscase, the signaling overhead for the partial subframe transmissionstarting position may be larger than in the above-described embodiment,but the flexibility for the starting time point of the transmission maybe increased. FIG. 25 shows an operation in which a user equipmentstarts transmitting a partial subframe for a base station in an SC-FDMAsymbol index in which the partial subframe is capable of including atleast one UL DM-RS.

The user equipment may receive the common control channel from the basestation to obtain information on the starting position of the partialsubframe transmission. In addition, when the user equipment receives theUL grant, the user equipment may receive a UE specific control channelfrom the base station to obtain information on the starting position ofthe partial subframe transmission. In addition, when the user equipmentreceives the common control channel and the UL grant, the user equipmentmay receive the UE specific control channel from the base station toobtain information on the starting position of the partial subframetransmission. In a specific embodiment, the control channel may be aPDCCH. As described above, when the user equipment is configured tostart partial subframe transmission for the base station at the slotboundary, the information on the starting position of the partialsubframe transmission may be 1-bit information. In addition, when theuser equipment starts the partial subframe transmission from the ULDM-RS transmission starting position as well as the slot boundary, theinformation on the starting position of the partial subframetransmission may be 2-bit information. Also, when the partial subframetransmission starting position is determined by the user equipment suchthat the partial subframe includes at least one DM-RS regardless ofwhether the partial subframe transmission starting position is the slotboundary or the SC-FDMA symbol position of the UL DM-RS, the informationon the starting position of the partial subframe transmission may be3-bit information.

The starting position and configuration of the starting partial subframethrough which the user equipment starts the physical channeltransmission have been described with reference to FIGS. 24 and 25. Thetransmission ending position and configuration of an ending partialsubframe through which a user equipment ends physical channeltransmission will be described with reference to FIGS. 26 and 27.

FIGS. 26 and 27 show that a user equipment is configured to receive anending partial subframe that ends a UL transmission from a base stationto perform a UL transmission to a base station according to anembodiment of the present invention.

Hereinafter, the transmitting the partial subframe may indicatetransmitting a physical channel in the partial subframe.

The user equipment may be configured by the base station to transmit apartial subframe including at least one UL DM-RS to the base station. Inthis case, the UL DM-RS may be a reference signal for demodulation ofthe data channel and the control channel transmitted through the UL. Inmore detail, the user equipment may end transmitting partial subframesto the base station at the slot boundary. In this case, the userequipment may transmit a partial subframe having 6 and 7 SC-FDMA symbolsas a duration. That is, when UL transmission that starts at the SC-FDMAsymbol index 1 is scheduled, the user equipment may transmit a partialsubframe having a duration of 6 SC-FDMA symbols in the first slot.Furthermore, when UL transmission that starts at the SC-FDMA symbolindex 0 is scheduled, the user equipment may transmit a partial subframehaving a duration of 7 SC-FDMA symbols at the boundary of the subframe.FIG. 26(a) shows an operation in which a user equipment ends partialsubframe transmission for a base station at a slot boundary.

In another specific embodiment, the user equipment may end transmissionof the partial subframe for the base station in at least one of the ULDM-RS transmission ending position as well as the slot boundary. In thiscase, the UL DM-RS may be a reference signal for demodulation of thedata channel and the control channel transmitted through the UL. In moredetail, the user equipment may end partial subframe transmission for thebase station after transmission of the SC-FDMA symbol, which is one ofthe SC-FDMA symbols transmitting the UL DM-RS and having the index 3 or10, as well as the slot boundary. FIG. 26(b) shows an operation in whicha user equipment ends partial subframe transmission for a base stationimmediately after transmission of a UL DM-RS as well as a slot boundary.

In another specific embodiment, the user equipment transmits a partialsubframe including at least one UL DM-RS to the base station regardlessof whether the transmission ending position of the partial subframe is aslot boundary or an SC-FDMA symbol position of the UL DM-RS. In thiscase, the signaling overhead for the ending position of the partialsubframe transmission may be larger than in the above-describedembodiment, but the flexibility for the transmission ending time pointmay be increased. FIG. 27 shows an operation in which a user equipmentends transmitting a partial subframe for a base station in an SC-FDMAsymbol index in which the partial subframe may include at least one ULDM-RS.

The user equipment may receive the common control channel from the basestation to obtain information on the ending position of the partialsubframe transmission. In addition, when the user equipment receives theUL grant, the user equipment may receive a UE specific control channelfrom the base station to obtain information on the ending position ofthe partial subframe transmission. In addition, when the user equipmentreceives the common control channel and the UL grant, the user equipmentmay receive the UE specific control channel from the base station toobtain information on the ending position of the partial subframetransmission. In a specific embodiment, the control channel may be aPDCCH. As described above, when the user equipment is configured by thebase station to end partial subframe transmission for the base stationat the slot boundary, the information on the ending position of thepartial subframe transmission may be 1-bit information. In addition,when the user equipment ends the partial subframe transmission at the ULDM-RS transmission ending position as well as the slot boundary, theinformation on the ending position of the partial subframe transmissionmay be 2-bit information. Also, when the ending position of the partialsubframe transmission is determined by the user equipment such that thepartial subframe includes at least one DM-RS regardless of whether theending position of the partial subframe transmission is the slotboundary or the SC-FDMA symbol position of the UL DM-RS, the informationon the starting position of the partial subframe transmission may be3-bit information.

Embodiments described with reference to FIGS. 24 to 27 may be applied toat least one of a case where a partial subframe is transmitted as astarting partial subframe, a case where a partial subframe istransmitted as an ending partial subframe, and a case where a partialsubframe is transmitted as a starting partial subframe and an endingpartial subframe.

The user equipment may determine a channel access operation startingtime point according to a time point for receiving signaling on astarting time point of a UL transmission from a base station.Accordingly, the partial subframe transmission starting position mayalso vary. In another specific embodiment, the user equipment maydetermine the channel access operation starting time point beforeobtaining information on the starting time point of the UL transmissionfrom the base station. The user equipment may receive, from the basestation, information on the starting time point of the UL transmissionindicating that the user equipment may start UL transmission at theboundary of the subframe and the second slot boundary. In this case,when the user equipment does not succeed in the channel access operationuntil the starting time point of the transmission, which is the boundaryof the subframe, the user equipment may attempt additional channelaccesses before the starting time point of the second slot, which is thestarting time point of the next UL transmission. In this case, thechannel access operation may indicate the LBT based channel operationsdescribed above. In a specific embodiment, the user equipment maydetermine the channel access operation starting time point according tothe time point for receiving signaling on the starting time point of theUL transmission from the base station. Accordingly, the partial subframetransmission starting position may also vary. In another specificembodiment, the user equipment may determine the channel accessoperation starting time point before the time point for receivingsignaling on the starting time point of the UL transmission from thebase station.

When the user equipment succeeds in channel access until the startingtime point of the transmission of the partial subframe, the partialsubframe may be transmitted. When the user equipment does not succeed inchannel access until the starting time point of the transmission of thepartial subframe, the user equipment may attempt channel access forpartial subframe transmission before another starting time point of thetransmission of the partial subframe configured by the base station inthe corresponding subframe. When another starting time point of partialsubframe transmission is not configured in the corresponding subframe bythe base station, the user equipment may not attempt to transmit thepartial subframe.

When the user equipment is not configured for transmission of thepartial subframe from the base station, the user equipment may performchannel access for UL transmission as follows. The base station mayindicate to the user equipment each of a starting time point for ULtransmission and a time point for ending UL transmission using a ULgrant. If the user equipment performs channel access after receiving theUL grant and does not succeed in channel access before the starting timepoint of the UL transmission, which is indicated by the corresponding ULgrant, the user equipment may not perform UL transmission in thecorresponding subframe according to the configuration by the basestation. However, when the UL transmission of the user equipmentcomposed of a plurality of subframes is scheduled by the base station,the user equipment may re-attempt channel access before the startingtime point of the next subframe in order for transmission in the nextsubframe after the subframe that fails in the channel access. In thiscase, when the user equipment succeeds in channel access, the userequipment may perform UL transmission from a subframe including astarting time point after the time point of successful channel access.

When the user equipment is not configured for transmission of thepartial subframe from the base station, the user equipment may determinewhether to re-attempt channel access by receiving whether a plurality ofsubframe UL transmissions are scheduled from the base station.Specifically, when the user equipment receives scheduling for aplurality of subframe UL transmissions from the base station and thechannel access is not successful until the scheduled starting time pointof the transmission, the user equipment may re-attempt to access thechannel. In this case, when the user equipment succeeds in channelaccess before the subframe boundary after the scheduled starting timepoint of the transmission, the user equipment may start the ULtransmission from the subframe boundary closest to the channel accesssuccess time point. Specifically, at the subframe boundary closest tothe channel access success time point, the user equipment may start thetransmission of the remaining subframes except for the subframe nottransmitted from the starting time point of the transmission at whichthe user equipment receives the scheduling to the nearest subframeboundary from the channel access success time point.

When the user equipment is configured for transmission of the partialsubframe from the base station, a method in which the user equipmentadditionally accesses a channel to perform UL transmission in a partialsubframe may be considered. If the user equipment is configured fortransmission of a partial subframe and the user equipment does notsucceed in channel access for UL transmission at the starting time pointof the UL subframe or the starting time point of the UL grant fortransmission of the UL subframe indicated by the UL grant, a method inwhich a user equipment performs additional channel access fortransmission of a partial subframe in a UL subframe will be describedbelow.

According to the setting of the base station, the user equipment maystart transmission of the starting partial subframe and configure apartial subframe as shown in FIGS. 24 to 25. In this case, when the userequipment performs channel access at the starting time point of the ULtransmission indicated by the UL grant from the base station and thenfails, the user equipment may additionally perform channel access beforethe starting time point indicated by the UL grant for UL transmission inthe next UL starting partial subframe. In this case, it is a matter ofwhich channel access parameter the user equipment uses while performingchannel access for UL transmission in the starting partial subframe.Specifically, it is a matter of which channel access type the userequipment should use to perform channel access for UL transmission inthe starting partial subframe. In addition, it is a matter of whichchannel access priority class the user equipment should use to performchannel access for UL transmission in the UL starting partial subframe.When the user equipment is configured for partial subframe transmissionfrom the base station, the user equipment may start the UL transmissionfor the base station at one or more time points within the subframeboundary and a subframe. In this case, the subframe boundary and one ormore time points within the subframe may be configured by the basestation. In more detail, the subframe boundary and one or more timepoints within the subframe may be indicated by the UL grant. When theuser equipment fails to access the channel until the initial startingtime point of the transmission, the user equipment may attempttransmission to the base station by attempting channel access before theremaining starting time points of the transmission other than theinitial starting time point of the transmission. When a user equipmentcan start UL transmission at a plurality of starting time points of theUL transmission in such a manner, the channel access type used by theuser equipment and the parameters related to channel access areproblematic.

In a specific embodiment, when a user equipment fails to access achannel and fails to start UL transmission at a initial starting timepoint of the transmission, the user equipment may attempt channel accessbefore the remaining starting time points of the transmission other thanthe starting time point. In this case, the user equipment may performchannel access using the channel access type indicated by the UL grantwith respect to UL transmission at the remaining starting time points ofthe transmission in the subframe to be transmitted. In addition, theuser equipment may perform channel access according to a channel accesspriority class indicated by a UL grant for a subframe to be transmitted.In this case, the UL grant may be a UL grant in which the user equipmentindicates UL transmission at the initial starting time point of thetransmission. In addition, the UL grant may be a UL grant indicating theUL transmission that the user equipment attempts after the initialstarting time point of the transmission. For example, when a userequipment fails to access a channel using a type 1 channel accessindicated by a UL grant and fails to start UL transmission until theinitial starting time point of the transmission, the user equipment mayattempt channel access using the type 1 channel access after the initialstarting time point of the transmission. When a user equipment fails toaccess a channel using a type 2 channel access indicated by a UL grantand fails to start UL transmission until the initial starting time pointof the transmission, the user equipment may attempt channel access usingthe type 2 channel access after the initial starting time point of thetransmission. In another specific embodiment, when a user equipmentfails to access a channel using a type 2 channel access indicated by aUL grant, fails to start UL transmission until the initial starting timepoint of the transmission, and the channel is idle continuously duringthe defer period after the initial starting time point of thetransmission, the user equipment may attempt channel access using thetype 2 channel access. In addition, when the user equipment fails toaccess the channel and fails to start UL transmission until the initialstarting time point of the transmission, the user equipment may performchannel access using the channel access priority class used for channelaccess before the initial starting time point of the transmission withrespect to UL transmission at the remaining starting time points of thetransmission in the subframe to be transmitted.

In another specific embodiment, when a user equipment fails to access achannel and fails to start UL transmission until the initial startingtime point of the transmission, the user equipment may attempt channelaccess before the remaining starting time points of the transmissionother than the initial starting time point. In this case, the userequipment may perform channel access based on the channel access typeused in the channel access until the initial starting time point of thetransmission. In more detail, when the user equipment fails to accessthe channel and fails to start UL transmission until the initialstarting time point of the transmission, the user equipment may performchannel access based on the channel access type used in the channelaccess until the initial starting time point of the transmissionregardless of the channel access type indicated by the UL grant. This isbecause the user equipment determines the channel access type accordingto the channel access type determination condition, so that the userequipment may be allowed to perform channel access according to the samechannel access type. In addition, the user equipment may perform channelaccess based on the channel access priority class used in the channelaccess before the initial starting time point of the transmission. Inmore detail, when the user equipment fails to access the channel andfails to start UL transmission until the initial starting time point ofthe transmission, the user equipment may perform channel access based onthe channel access priority class used in the channel access before theinitial starting time point of the transmission regardless of thechannel access priority class indicated by the UL grant.

In another specific embodiment, when a user equipment fails to access achannel and fails to start UL transmission until a initial starting timepoint of the transmission, the user equipment may attempt channel accessbefore the remaining starting time points of the transmission other thanthe initial starting time point. In this case, the user equipment maydetermine the channel access type used in channel access after theinitial starting time point of the transmission based on whether theuser equipment performs transmission in the MCOT. In more detail, theuser equipment may determine the channel access type based on whethertransmission is performed in the MCOT regardless of the channel accesstype indicated by the UL grant. In this case, when the user equipmentperforms transmission in the MCOT, the user equipment may performchannel access using channel access type 2. In addition, the userequipment may perform UL transmission based on the 2nd trigger throughthe C-PDCCH. In this case, the user equipment may determine the channelaccess type used in channel access after the initial starting time pointof the transmission based on whether the user equipment performstransmission within the UL duration set by the base station.Specifically, the user equipment may determine the channel access typeused in channel access after the initial starting time point of thetransmission based on whether the user equipment performs transmissionwithin the UL duration set by the base station, regardless of thechannel access type indicated by the UL grant. In this case, when theuser equipment performs transmission in the UL duration set by the basestation, the user equipment may perform channel access using the channelaccess type 2.

In another specific embodiment, when a user equipment fails to access achannel and fails to start UL transmission until a initial starting timepoint of the transmission, the user equipment may attempt channel accessbefore the remaining starting time points of the transmission other thanthe initial starting time point. In this case, the user equipment mayperform channel access based on the channel access type used in thechannel access until the initial starting time point of thetransmission. In this case, for example, when the user equipmentattempts to access the channel using the channel access type 2 and failsto access the channel thereby failing to start the UL transmission untilthe initial starting time point of the transmission, the user equipmentmay attempt channel access using the channel access type 2. In thiscase, when the channel is continuously idle for a predetermined timesection, the user equipment may attempt channel access using the channelaccess type 2. In addition, when the user equipment attempts to accessthe channel using the channel access type 2 and fails to access thechannel until the initial starting time point of the transmission, theuser equipment may attempt channel access using the channel access type2 until the starting time point of the UL transmission, which isintended by the user equipment or base station. In this case, when thechannel is continuously idle for a predetermined time interval, the userequipment may attempt channel access using the channel access type 2.

In another specific embodiment, when a user equipment fails to access achannel and fails to start UL transmission until the initial startingtime point of the transmission, the user equipment may attempt channelaccess before the remaining starting time points of the transmissionother than the initial starting time point. In this case, the userequipment may perform channel access using a predetermined channelaccess type regardless of the channel access type used in the channelaccess until the initial starting time point of the transmission.Specifically, the user equipment may perform channel access using apredetermined channel access type regardless of the channel access typeused by the user equipment for channel access until the initial startingtime point of the transmission and whether the user equipment performstransmission in the MCOT. In the above-described embodiments, thepredetermined channel access type may be the type 1 channel accessdescribed above. For example, when a user equipment fails to access achannel using the type 2 channel access and fails to start ULtransmission until the initial starting time point of the transmission,the user equipment may perform the type 1 channel access using a channelaccess priority class indicated by a UL grant indicating the type 2channel access. In such an embodiment, the user equipment may performtype 1 channel access to increase fairness for coexistence with otherwireless communication devices.

In the above-described embodiments, the MCOT may indicate the MCOTobtained by the base station. In the above-described embodiments, theMCOT may indicate the MCOT obtained by the user equipment.

In the above-described embodiments, when the user equipment succeeds inchannel access after the initial starting time point of thetransmission, the user equipment may perform UL transmission for thebase station from the remaining starting time point of the transmissionother than the initial starting time point of the transmission. In thiscase, when the user equipment receives the scheduling information on theUL transmission of the entire subframe by the UL grant, the userequipment may puncture the data channel scheduled to be transmittedbefore the starting time point of the UL transmission, and the userequipment may transmit the remaining data channel to the base stationfrom the remaining starting time points of the transmission other thanthe initial starting time point of the transmission.

In another specific embodiment, when the user equipment receives thescheduling information on the UL transmission of the entire subframe bythe UL grant, the user equipment may rate-match the data channelscheduled to be transmitted before the starting time point of the ULtransmission, and the user equipment may transmit the rate-matched datachannel to the base station from the remaining starting time points ofthe transmission other than the initial starting time point of thetransmission.

When the user equipment accesses the channel using a channel accessbased random backoff, the user equipment may adjust the size CWS of thecontention window based on whether the previously transmitted ULtransmission is successful or not. The user equipment may randomlyobtain any one of natural numbers from 0 to CW, and backoff for a timeinterval determined according to the obtained natural number. In thiscase, the probability that the user equipment obtains each of thenatural numbers from 0 to CW is the same. Therefore, the user equipmentmay adjust the CWS by adjusting the value of CW. In this case, thepreviously transmitted transmission may specifically indicate thetransmission of the previously transmitted subframe. For convenience ofdescription, a corresponding subframe is referred to as a referencesubframe in transmission of a subframe that is a reference of CWadjustment. In addition, an identifier ID for identifying an HARQprocess of the UL-SCH in the reference subframe is referred to as areference HARQ_PROCESS_ID. In this case, the UL-SCH is a data channelincluding user data. In more detail, when an NDI value for at least oneHARQ process associated with at least one reference HARQ_PROCESS_ID istoggled, the user equipment may reset a value of the CW for each of allchannel access priority classes by each class. When the user equipmentresets a value of the CW for each of all channel access priority classesby each class, the user equipment may set the value of the CW for eachof all channel access priority classes to the minimum value in acorresponding channel access priority class. When this is not the case,the user equipment may increase the value of the CW for each of allpriority classes to the next higher allowed value than the current valueof the CW among the allowable values of the priority class. In thiscase, the user equipment may maintain the value of the CW of thecorresponding channel access priority class when the current value ofthe CW is the largest value in the corresponding channel access priorityclass. In addition, when the user equipment receives the UL grant, thetoggle of the received NDI value may indicate that the transmissioncorresponding to the HARQ process associated with the correspondingHARQ_PROCESS_ID previously transmitted by the user equipment issuccessful. In addition, the toggle of the NDI value received whenreceiving the UL grant may indicate that scheduling from the currentlyreceived UL grant indicates new data.

The user equipment may determine the reference subframe n_(ref)according to the following rule. In more detail, the user equipment maydetermine a reference subframe n_(ref) based on a UL grant subframen_(g), which is a subframe for receiving a UL grant for the userequipment. According to a specific embodiment of the present invention,a user equipment may perform UL transmission including a UL-SCH by usinga channel access based random backoff, and determine, as the referencesubframe n_(ref), a subframe before the time point obtained bysubtracting a predetermined time interval from the subframe n_(g)transmitting the UL grant based on a UL transmission burst including themost recent subframe n_(w) among subframes for UL transmission. Thepredetermined time interval may be a duration of three subframes. Thatis, among the subframes transmitted by the user equipment before thetime point (before n_(g)−3) after subtracting the duration of threesubframes from the subframes n_(g) transmitting the UL grant, the mostrecent subframe transmitted by the user equipment may be a recentsubframe n_(w). In this case, among the subframes transmitted by theuser equipment before the duration (n_(g)−3) of three subframes based onthe subframe n_(g) transmitting the UL grant, the user equipment maydetermine the reference subframe n_(ref) based on the subframetransmitted most recently by the user equipment. Among subframes for ULtransmission before a predetermined time interval, which are ahead ofthe UL grant subframe n_(g), the UL transmission burst including themost recent subframe n_(w) is referred to as the reference ULtransmission burst. Among the subframes for UL transmission before thetime point obtained by subtracting a predetermined time interval fromthe subframe n_(g) transmitting the UL grant, when there are one or moresubframes that are continuous without a gap with the most recentsubframe n_(w) and are earlier than the most recent subframe n_(w), theuser equipment may determine, as the reference subframe n_(ref), thesubframe transmitted by the user equipment first among the correspondingone or more subframes. In addition, when the UL transmission burstincludes only one subframe, the user equipment may determine thecorresponding subframe n_(w) as the reference subframe n_(ref).

In addition, as described above, the user equipment may start ULtransmission at a time point that is not a subframe boundary. The userequipment may start uplink transmission based on one of an SC-FDMAsymbol having an index of 0 and an SC-FDMA symbol having an index of 7based on the subframe. Specifically, the user equipment may start uplinktransmission from at least one of the starting time point of the SC-FDMAsymbol having an index of 0, the time point obtained by adding 25 us tothe starting time point of the SC-FDMA symbol having an index of 0, thetime point obtained by adding Timing Advance (TA) to the time pointobtained by adding 35 us to the starting time point of the SC-FDMAsymbol having an index of 0, and the starting time point of the SC-FDMAsymbol having an index of 1. In addition, the user equipment may furtherstart uplink transmission from at least one of the starting time pointof the SC-FDMA symbol having an index of 7, the time point obtained byadding 25 us to the starting time point of the SC-FDMA symbol having anindex of 7, the time point obtained by adding TA to the time pointobtained by adding 35 us to the starting time point of the SC-FDMAsymbol having an index of 7, and the starting position of the SC-FDMAsymbol having an index of 8. In a specific embodiment, when the userequipment attempts to access a channel at a subframe starting time pointand the user equipment does not succeed in channel access until thesubframe starting time point according to the channel access result, theuser equipment may start the UL transmission at a specific time point inthe corresponding subframe. This UL transmission mode may be referred toas mode 1.

In addition, the user equipment may start the UL transmission accordingto the indication of the base station at a randomtime point between thestarting time point of the SC-FDMA symbol having an index 7 of theSC-FDMA symbol, and the starting time point of the SC-FDMA symbol havingan index 7 of the SC-FDMA symbol and the starting time point of theSC-FDMA symbol having an index of 8. In addition, as described above,the user equipment may further start uplink transmission from at leastone of the starting time point of the SC-FDMA symbol having an index of7, the time point obtained by adding 25 us to the starting time point ofthe SC-FDMA symbol having an index of 7, the time point obtained byadding TA to the time point obtained by adding 35 us to the startingtime point of the SC-FDMA symbol having an index of 7, and the startingposition of the SC-FDMA symbol having an index of 8. This ULtransmission mode may be referred to as mode 2. In various embodimentsincluding these embodiments, a partial subframe may be transmitted.Therefore, when the reference UL transmission burst includes a partialsubframe, a method of setting a reference subframe by the user equipmentis a problem. This will be described with reference to FIGS. 28 to 30.

FIGS. 28 to 30 show operation of determining, by a user equipment, areference subframe of CWS adjustment based on a subframe including an ULgrant.

When the reference subframe includes only partial subframes, even if theuser equipment succeeds in channel access, due to the short data lengthtransmitted through the partial subframe, the base station may fail todecode the data. Accordingly, the base station may set the NDIcorresponding to the partial subframe not to be toggled and request theuser equipment to re-transmit. In addition, in the case of the mode 1described in the embodiment of the present invention, data scheduling isreceived from the base station for the entire subframe but channelaccess may fail at the starting time point of the transmission near thesubframe boundary, and channel access may be successful before thetransmission position of the second slot. In this case, the userequipment may transmit UL data by puncturing part of the ULtransmission. Since part of the UL transmissions is punctured, it islikely that the base station fails to decode the UL transmissions of theuser equipment. In such a way, although the user equipment succeeds inchannel access, the value of the CW may increase due to the datadecoding failure of the base station. Therefore, when the referencesubframe includes the partial subframe, the user equipment needs toadditionally determine a subframe other than the partial subframe as thereference subframe.

When the reference UL transmission burst includes only a partialsubframe, the user equipment may determine the corresponding partialsubframe as the reference subframe. Specifically, among subframes for ULtransmission to subframes ahead of time points obtained by subtracting apredetermined time interval from the subframe n_(g) receiving the ULgrant, when the most recent subframe n_(w) is a partial subframe andthere is no continuous subframe without a gap with the partial subframe,the user equipment may determine the corresponding partial subframe as areference subframe. In the embodiment of FIG. 28, among subframes for ULtransmission to a subframe ahead of (before SF #n_(g)−3) the time pointobtained by subtracting three subframe durations from the subframe SF#n_(g) receiving the UL grant, the most recent subframe SF #n_(w) is apartial subframe, and there is no continuous subframe with thecorresponding partial subframe. Accordingly, among subframes for ULtransmission to a subframe ahead of (before SF #n_(g)−3) the threesubframe durations, which is other than the subframe SF #n_(g) receivingthe UL grant, the user equipment determines the partial subframe SF#n_(w), which is the most recent subframe, as a reference subframe.

When the reference UL transmission burst includes a partial subframe andat least one subframe and the partial subframe is the leading subframeno in the UL transmission burst, the user equipment may determine thesubframe immediately following the partial subframe as the referencesubframe in the partial subframe and the UL transmission burst.Specifically, among subframes for UL transmission to a subframe ahead ofthe time point obtained by subtracting a predetermined time interval,which is other than the subframe n_(g) receiving the UL grant, there areone or more subframes that are continuous with the most recent subframen_(w) and are ahead of the most recent subframe n_(w), and the earliestsubframe among the one or more subframes may be a partial subframe. Inthis case, the user equipment may determine the subframe immediatelyfollowing the corresponding partial subframe as the reference subframesin the corresponding partial subframe and at least one subframe. In suchembodiments, when NDI is toggled for at least one HARQ process among thereference HARQ process IDs associated with each of the earliest partialsubframe in the reference UL transmission burst and the subframeimmediately following the corresponding partial subframe in the ULtransmission burst, the user equipment may reset the value of the CW foreach channel access priority class to each channel access priorityclass's minimum value. In addition, when NDI is not toggled for at leastone HARQ process among the reference HARQ process IDs associated witheach of the earliest partial subframe in the reference UL transmissionburst and the subframe immediately following the corresponding partialsubframe in the UL transmission burst, the user equipment may increasethe value of the CW for each channel priority class to the next largervalue than the current value of the CW among the allowable values in thechannel priority class.

In the embodiment of FIG. 29, among subframes for UL transmission aheadof (before SF #n_(g)−3) the time point obtained by subtracting threesubframe durations from the subframe SF #n_(g) receiving the UL grant,there is at least one subframe that is continuous without a gap with themost recent subframe SF #n_(w) before the recent subframe SF #n_(w). Inthis case, the earliest subframe among the one or more subframes is thepartial subframe SF #no. Therefore, the user equipment determines thepartial subframe SF #no and the subframe SF #n₁ for UL transmissionimmediately following the partial subframe SF #no as the referencesubframes.

When the reference UL transmission burst includes a partial subframe andthe corresponding partial subframe is the earliest subframe in the ULtransmission burst including a partial subframe, the user equipment maydetermine the corresponding partial subframe and the subframeimmediately following the corresponding partial subframe as thereference subframes. Specifically, among subframes for UL transmissionahead of the time point obtained by subtracting a predetermined timeinterval from the subframe n_(g) transmitting the UL grant, the mostrecent subframe n_(w) is a partial subframe and there is no subframethat is continuous without a gap with a partial subframe and is for thepreceding UL transmission, but there may be at least one subframe thatis continuous with a partial subframe without a gap and is for thefollowing UL transmission. In this case, the user equipment maydetermine, as a reference subframe, a partial subframe that is the mostrecent subframe nw and a subframe immediately following thecorresponding partial subframe in one or more subframes. In suchembodiments, when NDI is toggled for at least one HARQ process among thereference HARQ process IDs associated with each of the earliest partialsubframe in the reference UL transmission burst and the subframeimmediately following the corresponding partial subframe in the ULtransmission burst, the user equipment may reset the value of the CW foreach channel access priority class to each channel access priorityclass's minimum value. In addition, when NDI is not toggled for at leastone HARQ process among the reference HARQ process IDs associated witheach of the earliest partial subframe in the reference UL transmissionburst and the subframe immediately following the corresponding partialsubframe in the UL transmission burst, the user equipment may increasethe value of the CW for each channel priority class to the next largervalue than the current value of the CW among the allowable values in thechannel priority class.

In the embodiment of FIG. 30(a), among subframes for UL transmissionahead of (before SF #n_(g)−3) the time point obtained by subtractingthree subframe durations from the subframe SF #n_(g) transmitting the ULgrant, the most recent subframe SF #n_(w) is a partial subframe. Also,there are one or more subframes that are continuous without a gap with apartial subframe. In this case, the user equipment may receive the NDIas HARQ feedback in consideration of the processing time for the ULreception of the base station for the UL transmission in the subframen_(w)+1. In this case, the user equipment determines the partialsubframe SF #n_(w) and the subframe SF #n_(w)+1 immediately followingthe partial subframe SF #n_(w) as a reference subframe.

In another specific embodiment, when the reference UL transmission burstincludes a partial subframe and the corresponding partial subframe isthe earliest subframe in the UL transmission burst including a partialsubframe, the user equipment may determine the corresponding partialsubframe as the reference subframe. Specifically, among subframes for ULtransmission ahead of the time point obtained by subtracting apredetermined time interval from the subframe ng transmitting the ULgrant, the most recent subframe n_(w) is a partial subframe and there isno subframe that is continuous without a gap with a partial subframe andis for the preceding UL transmission, but there may be at least onesubframe that is continuous with a partial subframe without a gap and isfor the following UL transmission. In this case, the user equipment maydetermine the corresponding partial subframe as a reference subframe. Insuch embodiments, when the NDI of the reference HARQ process IDassociated with the most leasing partial subframe in the reference ULtransmission burst is toggled, the user equipment may reset the value ofthe CW for each channel access priority class to its minimum value. Inaddition, when the NDI of the reference HARQ process ID associated withthe most leasing partial subframe in the reference UL transmission burstis not toggled, the user equipment may increase the value of the CW foreach channel priority class to the next larger value than the currentvalue of the CW among the allowable values in the channel priorityclass.

The user equipment may determine the partial subframe and the subframeimmediately following the partial subframe as the reference subframe. Insuch embodiments, when NDI is toggled for at least one HARQ processamong the reference HARQ process IDs associated with each of theearliest partial subframe in the reference UL transmission burst and thesubframe immediately following the corresponding partial subframe, theuser equipment may reset the value of the CW for each channel accesspriority class to its minimum value. In addition, when NDI is nottoggled for at least one HARQ process among the reference HARQ processIDs associated with each of the earliest partial subframe in thereference UL transmission burst and the subframe immediately followingthe corresponding partial subframe, the user equipment may increase thevalue of the CW for each channel priority class to the next larger valuethan the current value of the CW among the allowable values in thechannel priority class.

Like the embodiment of FIG. 30(a), in the embodiment of FIG. 30(b),among subframes for UL transmission ahead of the time point obtained bysubtracting three subframe durations from the subframe SF #n_(g)transmitting the UL grant, the most recent subframe SF #n_(w) is apartial subframe. Also, there may be one or more subframes that arecontinuous without a gap with a partial subframe. In this case, the userequipment may not receive the NDI as HARQ feedback in consideration ofthe processing time for the UL reception of the base station for the ULtransmission in the subframe n_(w)+1. In this case, the user equipmentdetermines the partial subframe SF #n_(w) as the reference subframe. Theuser equipment may access the channel based on the adjusted value of theCW according to the embodiments described with reference to FIGS. 28 to30. When the user equipment succeeds in channel access, the userequipment may perform UL transmission for the base station.

The embodiments described with reference to FIGS. 28 to 30 may also beapplied when the reference UL transmission burst is transmitted in mode1 among the above-described UL transmission modes. In addition, theembodiments described with reference to FIGS. 28 to 30 may also beapplied when the reference UL transmission burst is transmitted in mode2 among the above-described UL transmission modes. In addition, theembodiments described with reference to FIGS. 28 to 30 may be equallyapplicable to autonomous UL transmission (AUL) as well as schedule-basedUL transmission.

In addition, the control channel may support cross-carrier scheduling aswell as self-carrier scheduling. The DL control channel may be any oneof the above-described PDCCH and E-PDCCH. In addition, the DL datachannel may be PDSCH. The UL control channel may be a PUCCH. Inaddition, the UL data channel may be a PUSCH. Embodiments of theinvention described above may be applied to unlicensed bands as well asother frequency bands using radio resources after a contentionprocedure.

FIG. 31 is a flowchart illustrating an operation of a user equipmentaccording to an embodiment of the present invention.

The user equipment may perform uplink (UL) transmission including asingle or a plurality of subframes. In this case, the user equipment mayperform UL transmission to the base station in a partial subframe havinga duration shorter than one subframe duration according to at least oneof the indication of the base station and the channel access result. TheUL transmission may include transmission of a UL channel. In this case,the UL channel may be a PUSCH. In addition, the UL transmission mayinclude transmission of a reference signal. In this case, the referencesignal may be an SRS or UL DM-RS.

The user equipment attempts to access a channel (S3101). The userequipment may attempt to access the channel using type 1 channel accessor type 2 channel access. In this case, the type 1 channel access mayindicate a channel access based random backoff. In more detail, the type1 channel access may indicate a channel access method in which a userequipment obtains a random value in a contention window and accesses thechannel based on whether the channel is idle for a time intervaldetermined based on the random value obtained by the user equipment. Inmore detail, the type 1 channel access may indicate a channel accessmethod using the cat-4 LBT described above. In addition, the type 2channel access may indicate a channel access method in which a userequipment accesses a channel based on whether the channel is idle for apredetermined single time section. In this case, the predetermined timesection may be 25 us. In more detail, the type 2 channel access mayindicate a channel access using the cat-2 LBT described above. Thedetailed operation of the user equipment may follow the embodimentsdescribed with reference to FIGS. 14 to 16.

When the user equipment succeeds in the accessing the channel, the userequipment performs UL transmission to the base station in a partialsubframe based on at least one of an indication of the base station anda result of the accessing the channel (S3105). The duration of thepartial subframe may be smaller than the duration of one subframe asdescribed above. The duration of one subframe may be 1 ms.

As described above, the user equipment may transmit the first subframeof the UL transmission burst as a partial subframe. In addition, theuser equipment may transmit the last subframe of the UL transmissionburst as a partial subframe. In a specific embodiment, the userequipment may start transmission of the partial subframe for the basestation from at least one of the UL DM-RS transmission starting positionas well as the slot boundary. In this case, the UL DM-RS may be areference signal for demodulation of the data channel and the controlchannel transmitted in the UL transmission. In more detail, the userequipment may start transmission at one or more time points designatedbased on a subframe boundary and at least one time point designatedbased on one or more time points in the subframe.

In another specific embodiment, the user equipment may transmit apartial subframe including at least one UL DM-RS to the base stationregardless of whether the transmission starting position of a partialsubframe is a slot boundary.

In another specific embodiment, the user equipment may end transmissionof the partial subframe for the base station in at least one of the ULDM-RS transmission ending position as well as the slot boundary. In thiscase, the UL DM-RS may be a reference signal for demodulation of thedata channel and the control channel transmitted in the UL transmission.In more detail, the user equipment may start transmission at one or moretime points designated based on a subframe boundary and at least onetime point designated based on one or more time points in the subframe.

In another specific embodiment, in relation to the configuration of thepartial subframe, the user equipment configures the partial subframefrom the SC-FDMA index 0 to the SC-FDMA symbol having an SC-FDMA symbolindex of 3, 6, or 10, and transmits the partial subframe to the basestation. In this case, the user equipment may transmit aDemodulation-Reference Signal (DM-RS) at the position of the SC-FDMAsymbol having an index of 3 or 10 in the subframe.

In another specific embodiment, the user equipment may transmit apartial subframe including at least one UL DM-RS to the base stationregardless of whether the transmission ending position of a partialsubframe is a slot boundary.

In the above-described embodiments, the base station may signal theinformation on the starting position of the partial subframetransmission or the information on the ending position of the partialsubframe transmission using a common control channel. The user equipmentmay receive the common control channel from the base station to obtaininformation on the starting position of the partial subframetransmission or information on the ending position of the partialsubframe transmission ending position. In addition, the base station maysignal the information on the starting position of the partial subframetransmission or the information on the ending position of the partialsubframe transmission by using a UE specific control channel transmittedwhen the UL grant is transmitted. When the user equipment receives a ULgrant, the user equipment may receive a UE specific control channel fromthe base station to obtain information on the starting position of thepartial subframe transmission or information on the ending position ofthe partial subframe transmission. In addition, the base station maysignal the information on the starting position of the partial subframetransmission or the information on the ending position of the partialsubframe transmission by using the common control channel and a UEspecific control channel transmitted when the UL grant is transmitted.When the user equipment receives a common control channel and a ULgrant, the user equipment may receive a UE specific control channel fromthe base station to obtain information on the starting position of thepartial subframe transmission or information on the ending position ofthe partial subframe transmission. In addition, in a specificembodiment, the control channel may be a PDCCH. Also, the user equipmentmay perform specific operations regarding transmission start andtransmission end of a partial subframe according to the embodimentsdescribed with reference to FIGS. 23 to 27.

The UL grant may indicate that the user equipment is capable of startingtransmission at the subframe boundary and at one or more time pointswithin the subframe, and the user equipment may fail to access thechannel until the initial starting time point of the transmission. Inthis case, the user equipment may attempt UL transmission to the basestation before the remaining starting time points of the transmissionother than the initial starting time point of the transmission. In aspecific embodiment, after the initial starting time point of thetransmission, the user equipment may perform channel access using achannel access type indicated by a UL grant for a subframe to betransmitted. In another specific embodiment, after the initial startingtime point of the transmission, the user equipment may perform channelaccess based on the channel access type used in the channel access untilthe initial starting time point of the transmission.

In another specific embodiment, when the user equipment fails to accessthe channel and fails to start UL transmission to the base station untilthe initial starting time point of the transmission, the user equipmentmay determine the channel access type used for channel access after theinitial starting time point of the transmission based on whether theuser equipment performs transmission in the MCOT. In this case, the MCOTmay be set by the base station. Specifically, based on whether the userequipment performs transmission within the MCOT regardless of thechannel access type indicated by the UL grant indicating the ULtransmission for the base station, the user equipment may determine thechannel access type used for channel access after the initial startingtime point of the transmission. In this case, when the user equipmentperforms transmission in the MCOT, the user equipment may performchannel access using channel access type 2.

In another specific embodiment, when the user equipment fails to accessthe channel until the initial starting time point of the transmissionand fails to start UL transmission until the initial starting time pointof the transmission, the user equipment may perform channel access afterthe initial starting time point of the transmission based on the channelaccess type used in the channel access until the initial starting timepoint of the transmission. Specifically, regardless of the channelaccess type indicated by the UL grant indicating the UL transmissionafter the initial starting time point, the user equipment may access thechannel for UL transmission to the base station after the initialstarting time point of the transmission using the channel access typeused before the initial starting time point of the transmission. Thespecific operation of the user equipment with respect to channel accessmay follow the above-described embodiments.

When the user equipment accesses the channel using a channel accessbased random backoff, the user equipment may adjust the value of thecontention window used for the channel access based random backoff basedon whether a transmission of a reference subframe previously transmittedusing the channel access based random backoff is successful or not. Inthis case, the user equipment may attempt UL transmission to the basestation by accessing the channel based on the adjusted contentionwindow. In this case, the reference subframe may include the partialsubframe. In addition, the contention window may indicate a range inwhich a natural number that determines a backoff time in a procedure ofa channel access based random backoff is obtained randomly, and thevalue of the contention window may be the largest value among naturalvalues that determine the backoff time. In addition, the minimum valueof the contention window may be fixed to 0.

The earliest subframe among the first one or more subframes that arecontinuously transmitted without intervals before the subframes recentlytransmitted by the user equipment and perform UL transmission may be apartial subframe. In this case, the recently transmitted subframe is asubframe that is transmitted by the user equipment ahead of the timepoint obtained by subtracting a predetermined time interval from thestarting time point of the subframe including the UL grant and is mostrecently transmitted by the user equipment among the subframesperforming the UL transmission, and the UL grant may indicate ULtransmission for the base station attempting the transmission byaccessing a channel based on the size of the contention window. In thiscase, the user equipment may determine, as the reference subframe, theearliest subframe and the subframe transmitted by the user equipmentimmediately following the earliest subframe among one or more firstsubframes.

When the recently transmitted subframe is the partial subframe and thereare no one or more first subframes, the user equipment may determineonly the recently transmitted subframe as the reference subframe.

The recently transmitted subframe may be a partial subframe, there maybe no one or more first subframes, and there may be one or more secondsubframes that are transmitted by the user equipment continuouslywithout a gap after a recently transmitted subframe and perform ULtransmission. In this case, however, the recently transmitted subframeand a subframe following the recently transmitted subframe among the oneor more second subframes may be determined as the reference subframe.

When a new data indicator (NDI) for at least one HARQ process associatedwith at least one reference HARQ process ID is toggled, the userequipment may set the value of the contention window of all channelaccess priority classes to the minimum value of the value of thecontention window corresponding to each of the corresponding channelaccess priority classes. In this case, the reference HARQ process ID maybe an identifier for identifying the HARQ process of the UL-SCH in thereference subframe. In addition, when an NDI for at least one HARQprocess associated with at least one reference HARQ process ID is nottoggled, the user equipment may increase the size of the contentionwindow of all channel access priority classes to the next larger valuethan the current contention window value among the values allowed in thechannel access priority class. In this case, if the value of the currentcontention window is the largest value among the contention windowvalues allowed in the corresponding channel access priority class, theuser equipment may maintain the contention window value of thecorresponding channel access priority class as it is.

FIG. 32 illustrates a configuration of a user equipment and a basestation according to an embodiment of the present invention. Theembodiment of the present invention, the user equipment may beimplemented by various types of wireless communication devices orcomputing devices that are guaranteed to be portable and mobility. Theuser equipment may be referred to as a station (STA), an MobileSubscriber (MS), or the like. In the embodiment of present invention,the base station may control and manage a cell (eg, macrocell,femtocell, picocell, etc.) corresponding to a service area and performfunction such as transmitting signal, designating channel, monitoringchannel, self-diagnosis, relay. The base station may be referred to asan evolved NodeB (eNB), an access point (AP), or the like.

Referring to the figure, the user equipment 100 may include a processor110, a communication module 120, a memory 130, a user interface unit140, and a display unit 150.

The processor 110 may execute various commands or programs according tothe present invention and process data in the user equipment 100.Further, the processor 100 may control all operations of the respectiveunits of the user equipment 100 and control data transmission/receptionamong the units. For example, the processor 110 may receive/process thedownlink signal according to the proposal of the present invention.

The communication module 120 may be an integrated module that performsmobile communication using a mobile communication network and wirelessLAN access using a wireless LAN. To this end, the communication module120 may include a plurality of network interface cards such as cellularcommunication interface cards 121 and 122 and a wireless LAN interfacecard 123 in an internal or external type. In the figure, thecommunication module 120 is illustrated as the integrated module, butthe respective network interface cards may be independently disposedaccording to a circuit configuration or a purpose unlike the figure.

The cellular communication interface card 121 transmits/receives a radiosignal to/from at least one of a base station 200, an external device,and a server by using the mobile communication network and provides acellular communication service at a first frequency band based on acommand of the processor 110. The cellular communication interface card121 may include at least one NIC module using an LTE-licensed frequencyband. The cellular communication interface card 122 transmits/receivesthe radio signal to/from at least one of the base station 200, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at a secondfrequency band based on the command of the processor 110. The cellularcommunication interface card 122 may include at least one NIC moduleusing an LTE-unlicensed frequency band. For example, the LTE-unlicensedfrequency band may be a band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 123 transmits/receives the radio signalto/from at least one of the base station 200, the external device, andthe server through wireless LAN access and provides a wireless LANservice at the second frequency band based on the command of theprocessor 110. The wireless LAN interface card 123 may include at leastone NIC module using a wireless LAN frequency band. For example, thewireless LAN frequency band may be an unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

The memory 130 stores a control program used in the user equipment 100and various resulting data. The control program may include a programrequired for the user equipment 100 to perform wireless communicationwith at least one of the base station 200, the external device, and theserver. The user interface 140 includes various types of input/outputmeans provided in the user equipment 100. The display unit 150 outputsvarious images on a display screen.

Further, the base station 200 according to the exemplary embodiment ofthe present invention may include a processor 210, a communicationmodule 220, and a memory 230.

The processor 210 may execute various commands or programs according tothe present invention and process data in the base station 200. Further,the processor 210 may control all operations of the respective units ofthe base station 200 and control data and control channeltransmission/reception among the units. For example, the processor 210may transmit/process the downlink transmission of data and controlchannel according to the proposal of the present invention. For example,transmission of control channel and used data is performed according tothe FIGS. 17 to 23.

The communication module 220 may be an integrated module that performsthe mobile communication using the mobile communication network and thewireless LAN access using the wireless LAN like the communication module120 of the user equipment 100. To this end, the communication module 120may include a plurality of network interface cards such as cellularcommunication interface cards 221 and 222 and a wireless LAN interfacecard 223 in the internal or external type. In the figure, thecommunication module 220 is illustrated as the integrated module, butthe respective network interface cards may be independently disposedaccording to the circuit configuration or the purpose unlike the figure.

The cellular communication interface card 221 transmits/receives theradio signal to/from at least one of the user equipment 100, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at the firstfrequency band based on a command of the processor 210. The cellularcommunication interface card 221 may include at least one NIC moduleusing the LTE-licensed frequency band. The cellular communicationinterface card 222 transmits/receives the radio signal to/from at leastone of the user equipment 100, the external device, and the server byusing the mobile communication network and provides the cellularcommunication service at the second frequency band based on the commandof the processor 210. The cellular communication interface card 222 mayinclude at least one NIC module using the LTE-unlicensed frequency band.The LTE-unlicensed frequency band may be the band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 223 transmits/receives the radio signalto/from at least one of the user equipment 100, the external device, andthe server through the wireless LAN access and provides the wireless LANservice at the second frequency band based on the command of theprocessor 210. The wireless LAN interface card 223 may include at leastone NIC module using the wireless LAN frequency band. For example, thewireless LAN frequency band may be the unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

In the figure, blocks of the user equipment and the base stationlogically divide and illustrate elements of the device. The elements ofthe device may be mounted as one chip or a plurality of chips accordingto design of the device. Further, some components of the user equipment100, that is to say, the user interface 140 and the display unit 150 maybe selectively provided in the user equipment 100. Further, somecomponents of the base station 200, that is to say, the wireless LANinterface 223, and the like may be selectively provided in the basestation 200. The user interface 140 and the display unit 150 may beadditionally provided in the base station 200 as necessary.

The method and the system of the present invention are described inassociation with the specific embodiments, but some or all of thecomponents and operations of the present invention may be implemented byusing a computer system having a universal hardware architecture.

The description of the present invention is used for illustration andthose skilled in the art will understand that the present invention canbe easily modified to other detailed forms without changing thetechnical or an essential feature thereof. Therefore, the aforementionedexemplary embodiments are all illustrative in all aspects and are notlimited. For example, each component described as a single type may beimplemented to be distributed and similarly, components described to bedistributed may also be implemented in a combined form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

1-20. (canceled)
 21. A user equipment of a wireless communicationsystem, the user equipment comprising: a communication module; and aprocessor, wherein the processor is configured to: perform, in anunlicensed band, a uplink (UL) transmission including a single or aplurality of subframes by using the communication module, perform, inthe unlicensed band, a UL transmission in a partial subframe having aduration shorter than a duration of one subframe to a base stationaccording to at least one of an indication of the base station and aresult of a channel access of the user equipment, when the userequipment accesses a channel in the unlicensed band using a randombackoff based channel access, adjust a size of a contention window usedin the random backoff based channel access based on whether atransmission of a reference subframe previously transmitted by the userequipment using the random backoff based channel access is successful ornot, and perform, in the unlicensed band, a UL transmission to the basestation by accessing the channel based on the size of the contentionwindow, wherein the reference subframe comprises the partial subframe,wherein a backoff time in a procedure of the random backoff basedchannel access is determined based on a random number uniformlydistributed within 0 and the size of the contention window.
 22. The userequipment of claim 21, wherein the processor is configured to: when anearliest subframe among a plurality of subframes that are continuouslytransmitted without a gap by the user equipment in the unlicensed bandis the partial subframe, determine, as the reference subframe, theearliest subframe and a subframe transmitted by the user equipmentimmediately after the earliest subframe among the plurality ofsubframes, wherein a most recently transmitted subframe among theplurality of subframes is a subframe that is transmitted most recentlyby the user equipment among subframes that are transmitted by the userequipment before a time point obtained by subtracting a predeterminedtime interval from a starting time point of a subframe including a ULgrant, wherein the UL grant indicates a UL transmission to the basestation, which is attempted by accessing the channel based on a size ofthe contention window.
 23. The user equipment of claim 22, wherein whenthe plurality of subframes only include the most recently transmittedsubframe, the processor is configured to determine only the mostrecently transmitted subframe in the unlicensed band as the referencesubframe.
 24. The user equipment of claim 21, wherein when a new dataindicator (NDI) for at least one HARQ process associated with at leastone reference hybrid automatic repeat request (HARQ) process identifier(ID) is toggled, the processor is configured to set a size of acontention window of all channel access priority classes to a minimumsize of a size of a contention window corresponding to each channelaccess priority classes, wherein the reference HARQ process ID is anidentifier for identifying an HARQ process of a UL-SCH in the referencesubframe.
 25. The user equipment of claim 21, wherein when a new dataindicator (NDI) for at least one HARQ process associated with at leastone reference hybrid automatic repeat request (HARQ) process identifier(ID) is not toggled, the processor is configured to increase a size of acontention window of all channel access priority classes to the nextgreater size than a current size of a contention window among sizesallowed in a corresponding channel access priority class.
 26. The userequipment of claim 21, wherein when a UL grant indicates that the userequipment is capable of starting a UL transmission, in the unlicensedband, to the base station at a subframe boundary and one or morestarting time points of transmission in a subframe, and the userequipment fails to access the channel to start a UL transmission, in theunlicensed band, to the base station until an initial starting timepoint of transmission, the processor is configured to attempt a channelaccess for a UL transmission, in the unlicensed band, to the basestation before remaining starting time points of transmission other thanthe initial starting time point of transmission.
 27. The user equipmentof claim 26, wherein when the user equipment fails to access the channelto start the UL transmission to the base station until the initialstarting time point of transmission, the processor is configured todetermine a channel access type used in the channel access for a ULtransmission to the base station after the initial starting time pointof transmission based on whether the user equipment performs the ULtransmission, in the unlicensed band, within a maximum channel occupancytime (MCOT) configured by the base station.
 28. The user equipment ofclaim 27, wherein when the user equipment fails to access the channel tostart the UL transmission to the base station until the initial startingtime point of transmission and the user equipment performs thetransmission within the MCOT configured by the base station, theprocessor is configured to attempt to access the channel for the ULtransmission to the base station based on whether the channel is idlefor a predetermined single time interval, in the unlicensed band, afterthe initial starting time point of transmission.
 29. The user equipmentof claim 27, wherein when the user equipment fails to access the channelto start the UL transmission, in the unlicensed band, to the basestation until the initial starting time point of transmission, theprocessor is configured to determine a channel access type used in thechannel access for the UL transmission to the base station after theinitial starting time point of transmission based on whether the userequipment performs the UL transmission in the MCOT configured by thebase station, regardless of the channel access type indicated by a ULgrant indicating the UL transmission after the initial starting timepoint of transmission from the base station.
 30. The user equipment ofclaim 26, wherein when the user equipment fails to access the channel tostart the UL transmission to the base station until the initial startingtime point of transmission, the processor is configured to access thechannel for the UL transmission to the base station after the initialstarting time point of transmission by using a channel access type usedin the channel access for the UL transmission to the base station untilthe initial starting time point of transmission, regardless of thechannel access type indicated by a UL grant indicating the ULtransmission after the initial starting time point of transmission fromthe base station.
 31. The user equipment of claim 27, wherein thechannel access type comprises a first type indicating a random backoffbased channel access and a second type indicating channel access inwhich channel access is performed based on whether the channel is idlefor a predetermined single time interval.
 32. The user equipment ofclaim 21, wherein when the user equipment transmits a last subframe of aUL transmission, in the unlicensed band, to the base station as thepartial subframe, the processor is configured to configure the partialsubframe composed of the number of SC-FDMA symbols starting from aSingle Carrier (SC)-Frequency Division Multiple Access (FDMA) symbolindex 0 to an SC-FDMA symbol index of 3, 6, or 10, and ends the ULtransmission to the base station by transmitting the configured partialsubframe.
 33. The user equipment of claim 32, wherein the processor isconfigured to transmit a Demodulation-Reference Signal (DM-RS) at anSC-FDMA symbol position having an SC-FDMA symbol index of 3 or 10 in asubframe.
 34. An operation method of a user equipment of a wirelesscommunication system, the method comprising: performing, in anunlicensed band, uplink (UL) transmission including a single or aplurality of subframes, wherein the performing the UL transmissioncomprises performing the UL transmission in a partial subframe having aduration shorter than a duration of one subframe to a base stationaccording to at least one of an indication of the base station and aresult of a channel access of the user equipment, when the userequipment accesses a channel in the unlicensed band using a randombackoff based channel access, adjusting a size of a contention windowused in the random backoff based channel access based on whether atransmission of a reference subframe previously transmitted by the userequipment using the random backoff based channel access is successful ornot, and performing, in the unlicensed band, a UL transmission to thebase station by accessing the channel based on the size of thecontention window, wherein the reference subframe comprises the partialsubframe, wherein a backoff time in a procedure of the random backoffbased channel access is determined based on a random number uniformlydistributed within 0 and the size of the contention window.
 35. Themethod of claim 34, wherein the adjusting the size of the contentionwindow comprises, when the earliest subframe a plurality of subframesthat are continuously transmitted without a gap by the user equipment inthe unlicensed band is the partial subframe, determining, as thereference subframe, a subframe transmitted by the user equipmentimmediately after the earliest subframe among the plurality ofsubframes, wherein a most recently transmitted subframe among theplurality of subframes is a subframe that is transmitted most recentlyby the user equipment among subframes that are transmitted by the userequipment before a time point obtained by subtracting a predeterminedtime interval from a starting time point of a subframe including a ULgrant, wherein the UL grant indicates a UL transmission to the basestation, which is attempted by accessing a channel based on the size ofthe contention window.
 36. The method of claim 35, wherein the adjustingthe size of the contention window further comprises, when the pluralityof subframes only include the most recently transmitted subframe,determining only the most recently transmitted subframe in theunlicensed band as the reference subframe.